cmd/compile: move {SHL,SHR,SAR}X rules to late lower pass

cmd/compile: move {SHL,SHR,SAR}X rules to late lower pass

This can reduce a bunch of rules.

Change-Id: Id7d644307c295a0ed16eb837b3755d1117a4fbf7
Reviewed-on: https://go-review.googlesource.com/c/go/+/440036
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Wayne Zuo <wdvxdr@golangcn.org>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>