Unscaled memory operations were missing disassembly output for vector registers,
so add support and rewrite as a macro.

Bug: 
Change-Id: I6f388952dbe5a3b9f8a9b9c46e69ef63dc6655ba
Reviewed-on: https://chromium-review.googlesource.com/576177Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Cr-Commit-Position: refs/heads/master@{#46785}