The current implementation for Power architecture does not include the vector
(Altivec) registers.  This adds the 32 VMX registers and the most commonly used
instructions: X-form loads/stores; VX-form logical operations, add/sub,
rotate/shift, count, splat, SHA Sigma and AES cipher; VC-form compare; and
VA-form permute, shift, add/sub and select.

Fixes #15619

Change-Id: I544b990631726e8fdfcce8ecca0aeeb72faae9aa
Reviewed-on: https://go-review.googlesource.com/25600
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Reviewed-by: David Chase <drchase@google.com>