ppc: [liftoff] implement basic type conversion

Change-Id: I1cfb706a429a67830640ec3274b95dd6ee9cdd56
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3164904


Reviewed-by: Milad Fa <mfarazma@redhat.com>
Commit-Queue: Junliang Yan <junyan@redhat.com>
Cr-Commit-Position: refs/heads/main@{#76883}