For load extends, we can use Ldr, which does not require us to manually
calculate address - ld1r uses post-index, so we have to add the index
ourselves.

By checking the operation in the instruction-selector, we can set the
addressing mode for load extends to be MRR, then use Ldr in the codegen.

Bug: v8:9886
Change-Id: Ibcd22fa719cd6dafd2fd06e68066960db249b57a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2207656Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67912}