cmd/compile: add unsigned power-of-two detector

cmd/compile: add unsigned power-of-two detector

Fixes #74485

Change-Id: Ia22a58ac43bdc36c8414d555672a3a3eafc749ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/689815
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>