Currently we only correctly disassemble encoding A4, with a list of 4
regs.

Also added tests for these encodings.

Change-Id: I38066186d19deb8c180129d7a92b49bc589315cd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2554258Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71350}