cmd/compile/internal/ppc64, runtime internal/atomic, sync/atomic: implement faster atomics for ppc64x

This change implements faster atomics for ppc64x based on the ISA 2.07B,
Appendix B.2 recommendations, replacing SYNC/ISYNC by LWSYNC in some
cases.

Updates #21348

name                                           old time/op new time/op    delta
Cond1-16                                           955ns     856ns      -10.33%
Cond2-16                                          2.38µs    2.03µs      -14.59%
Cond4-16                                          5.90µs    5.44µs       -7.88%
Cond8-16                                          12.1µs    11.1µs       -8.42%
Cond16-16                                         27.0µs    25.1µs       -7.04%
Cond32-16                                         59.1µs    55.5µs       -6.14%
LoadMostlyHits/*sync_test.DeepCopyMap-16          22.1ns    24.1ns       +9.02%
LoadMostlyHits/*sync_test.RWMutexMap-16            252ns     249ns       -1.20%
LoadMostlyHits/*sync.Map-16                       16.2ns    16.3ns         ~
LoadMostlyMisses/*sync_test.DeepCopyMap-16        22.3ns    22.6ns         ~
LoadMostlyMisses/*sync_test.RWMutexMap-16          249ns     247ns       -0.51%
LoadMostlyMisses/*sync.Map-16                     12.7ns    12.7ns         ~
LoadOrStoreBalanced/*sync_test.RWMutexMap-16      1.27µs    1.17µs       -7.54%
LoadOrStoreBalanced/*sync.Map-16                  1.12µs    1.10µs       -2.35%
LoadOrStoreUnique/*sync_test.RWMutexMap-16        1.75µs    1.68µs       -3.84%
LoadOrStoreUnique/*sync.Map-16                    2.07µs    1.97µs       -5.13%
LoadOrStoreCollision/*sync_test.DeepCopyMap-16    15.8ns    15.9ns         ~
LoadOrStoreCollision/*sync_test.RWMutexMap-16      496ns     424ns      -14.48%
LoadOrStoreCollision/*sync.Map-16                 6.07ns    6.07ns         ~
Range/*sync_test.DeepCopyMap-16                   1.65µs    1.64µs         ~
Range/*sync_test.RWMutexMap-16                     278µs     288µs       +3.75%
Range/*sync.Map-16                                2.00µs    2.01µs         ~
AdversarialAlloc/*sync_test.DeepCopyMap-16        3.45µs    3.44µs         ~
AdversarialAlloc/*sync_test.RWMutexMap-16          226ns     227ns         ~
AdversarialAlloc/*sync.Map-16                     1.09µs    1.07µs       -2.36%
AdversarialDelete/*sync_test.DeepCopyMap-16        553ns     550ns       -0.57%
AdversarialDelete/*sync_test.RWMutexMap-16         273ns     274ns         ~
AdversarialDelete/*sync.Map-16                     247ns     249ns         ~
UncontendedSemaphore-16                           79.0ns    65.5ns      -17.11%
ContendedSemaphore-16                              112ns      97ns      -13.77%
MutexUncontended-16                               3.34ns    2.51ns      -24.69%
Mutex-16                                           266ns     191ns      -28.26%
MutexSlack-16                                      226ns     159ns      -29.55%
MutexWork-16                                       377ns     338ns      -10.14%
MutexWorkSlack-16                                  335ns     308ns       -8.20%
MutexNoSpin-16                                     196ns     184ns       -5.91%
MutexSpin-16                                       710ns     666ns       -6.21%
Once-16                                           1.29ns    1.29ns         ~
Pool-16                                           8.64ns    8.71ns         ~
PoolOverflow-16                                   1.60µs    1.44µs      -10.25%
SemaUncontended-16                                5.39ns    4.42ns      -17.96%
SemaSyntNonblock-16                                539ns     483ns      -10.42%
SemaSyntBlock-16                                   413ns     354ns      -14.20%
SemaWorkNonblock-16                                305ns     258ns      -15.36%
SemaWorkBlock-16                                   266ns     229ns      -14.06%
RWMutexUncontended-16                             12.9ns     9.7ns      -24.80%
RWMutexWrite100-16                                 203ns     147ns      -27.47%
RWMutexWrite10-16                                  177ns     119ns      -32.74%
RWMutexWorkWrite100-16                             435ns     403ns       -7.39%
RWMutexWorkWrite10-16                              642ns     611ns       -4.79%
WaitGroupUncontended-16                           4.67ns    3.70ns      -20.92%
WaitGroupAddDone-16                                402ns     355ns      -11.54%
WaitGroupAddDoneWork-16                            208ns     250ns      +20.09%
WaitGroupWait-16                                  1.21ns    1.21ns         ~
WaitGroupWaitWork-16                              5.91ns    5.87ns       -0.81%
WaitGroupActuallyWait-16                          92.2ns    85.8ns       -6.91%

Updates #21348

Change-Id: Ibb9b271d11b308264103829e176c6d9fe8f867d3
Reviewed-on: https://go-review.googlesource.com/95175
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>