P9 has vector insert instructions which could be used
for splatting 64bit inputs.

Change-Id: I16165271fd70848699430e1f77a1603d1023da49
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2611044Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#71929}