cmd/compile,cmd/internal/obj/ppc64: use mod instructions on power9

This updates the PPC64.rules file to use the MOD instructions
that are available in power9. Prior to power9 this is done
using a longer sequence with multiply and divide.

Included in this change is removal of the REM* opcode variations
that set the CC or OV bits since their settings are based
on the DIV and are not appropriate for the REM.

Change-Id: Iceed9ce33e128e1911c15592ee674276ce8ba3fa
Reviewed-on: https://go-review.googlesource.com/c/go/+/229761


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>