cmd/asm: add alias for MOVOA=MOVO on amd64

The alias should exist for both 386 and amd64.
There were a few others missing as well. Add them.

Change-Id: Ia0c3e71abc79f67a7a66941c0d932a8d5d6e9989
Reviewed-on: https://go-review.googlesource.com/5800


Reviewed-by: Russ Cox <rsc@golang.org>