[release-branch.go1.16] cmd/compile: fix simplification rules on arm/arm64

[release-branch.go1.16] cmd/compile: fix simplification rules on arm/arm64

Fixes #48474

Change-Id: Ic1e918f916eae223a3b530a51a58f03031924670
Reviewed-on: https://go-review.googlesource.com/c/go/+/350913
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/351072
Reviewed-by: Austin Clements <austin@google.com>