cmd/compile: fix register masks of ANDCC et al. on PPC64

PPC64's ANDCC, ORCC, XORCC SSA ops produce a flags value, which
should not have register mask of an integer register.

Fixes #34468.

Change-Id: Ic762e423b20275fd9f8118dae7951c258d59738c
Reviewed-on: https://go-review.googlesource.com/c/go/+/196960


Reviewed-by: Keith Randall <khr@golang.org>