The MOVI instruction writes an immediate into every lane of a vector. In
order to support all immediates, we split it into two 64-bit
writes. However if the top and bottom 64 bits are identical, we can skip
the second write.

Bug: v8:11033
Change-Id: Idfb74471de815d278a84c78d204d534d19214b2c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2507691Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Pierre Langlois <pierre.langlois@arm.com>
Cr-Commit-Position: refs/heads/master@{#70987}