cmd/compile: enable reg args and add duffcopy support on ppc64x
This adds support for duffcopy on ppc64x and updates the
ssa/config.go file to enable register args and recognize
the duffDevice is available on ppc64x.
Change-Id: Ifc472cc9cc19c9a80e468fb52078c75f7dd44d36
Reviewed-on: https://go-review.googlesource.com/c/go/+/351490
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Lynn Boger <laboger@linux.vnet.ibm.com> Reviewed-by: Cherry Mui <cherryyz@google.com>