cmd/compile: intrinsify runtime/internal/atomic.{And,Or} on PPC64

cmd/compile: intrinsify runtime/internal/atomic.{And,Or} on PPC64

This is a simple case of changing the operand size of the existing 8-bit
And/Or.

I've also updated a few operand descriptions that were out-of-sync with
the implementation.

Change-Id: I95ac4445d08f7958768aec9a233698a2d652a39a
Reviewed-on: https://go-review.googlesource.com/c/go/+/263150
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>