cmd/internal/obj/ppc64: generate smaller machine code for OR/XOR of uint32 values

cmd/internal/obj/ppc64: generate smaller machine code for OR/XOR of uint32 values

These binary operations can be done in two sequential instructions instead of loading a
constant into REGTMP and doing the binary op.

Change-Id: Ie0ab863f9e81afad140b92b265bca4d3f0fe90b1
Reviewed-on: https://go-review.googlesource.com/c/go/+/565215
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Run-TryBot: Paul Murphy <murp@ibm.com>