cmd/compile: use ellipses in ARM64 rules

Also, explicitly zero AuxInt in some ops (like Div),
to make it clear why they do not use an ellipsis.

Passes toolstash-check -all.

Change-Id: Iea0e807949f0899c43d2d21b9551a2cf00a829b3
Reviewed-on: https://go-review.googlesource.com/c/go/+/217006


Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>