Add several instructions that were used via BYTE and use them.
Instructions added: PEXTRB, PEXTRD, PEXTRQ, PINSRB, XGETBV, POPCNT.

Change-Id: I5a80cd390dc01f3555dbbe856a475f74b5e6df65
Reviewed-on: https://go-review.googlesource.com/18593
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>