cmd/asm, cmd/internal/obj/ppc64: add Immediate Shifted opcodes for ppc64x

This change adds ADD/AND/OR/XOR Immediate Shifted instructions for
ppc64x so they are usable in Go asm code. These instructions were
originally present in asm9.go, but they were only usable in that
file (as -AADD, -AANDCC, -AOR, -AXOR). These old mnemonics are now
removed.

Updates #23845

Change-Id: Ifa2fac685e8bc628cb241dd446adfc3068181826
Reviewed-on: https://go-review.googlesource.com/94115


Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>