cmd/compile: use | in the most repetitive ppc64 rules

cmd/compile: use | in the most repetitive ppc64 rules

For now, limited to the most repetitive rules that are also short and
simple, so that we can have a substantial conciseness win without
compromising rules readability.

Ran rulegen, no changes in the rewrite files.

Change-Id: I8d8cc67d02faca4756cc02402b763f1645ee31de
Reviewed-on: https://go-review.googlesource.com/95935
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>