Update the ppc64x disassembly code for use by objdump
from golang.org/x/arch/ppc64/ppc64asm commit fcea5ea.
Enable the objdump testcase for external linking on ppc64le
make a minor fix to the expected output.

Fixes #17447

Change-Id: I769cc7f8bfade594690a476dfe77ab33677ac03b
Reviewed-on: https://go-review.googlesource.com/32015
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>