cmd/asm,cmd/internal/obj/ppc64: update instructions and tests

cmd/asm,cmd/internal/obj/ppc64: update instructions and tests

This change adds some instructions that were missing from the
ppc64 assembler, mostly power9 but a few others from earlier.

Tests in cmd/asm for ppc64 were updated: ppc64.s includes the
new instructions, and ppc64enc.s now includes not only the
new instructions but most ppc64 opcodes to provide a more
complete test of the ppc64 assembler.

The ppc64 instruction set is used for linux/ppc64le,
linux/ppc64, and aix/ppc64.

Change-Id: I8695f89dbca06174847963f4ef869f2e584d5bbf
Reviewed-on: https://go-review.googlesource.com/c/go/+/229479
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Carlos Eduardo Seo <cseo@linux.vnet.ibm.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>