This CL adds a new vector scratch reg to PPC (v15)
and uses it during Simd swap operations.

Functions are also changed to accept scratch registers
as input.

Change-Id: I0220504ddf154148d2b83207b42ab2b7a794698c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3763863Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Farazmand <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/main@{#81733}