Combines 2 ldrs into a single ldm (without writeback since the
instruction uses fp as base and as a target). Shrinks the builtin
instruction size on ARM by 2932 bytes.

Change-Id: Id74e1e158a9d5db49caa2927e88df2a350adafab
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2011103Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65882}