load_extend is now implanted on BE machines by loading
bytes and using replace_lane to add it to the desired lane.

Interpret is also fixed to write lanes in reverse.

Change-Id: I984ae6b4bd41544fbf65c702a4b5b50ba03cb261
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2210147
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Reviewed-by: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67935}