P10 comes with prefixed instruction (2 x 4-byte instructions)
which allow for using larger immediate values. `paddi` has
been added in this CL which uses a 34-bit immediate.

Prefixed instructions cannot cross 64-byte boundaries, i.e we cannot
have the first 4-bytes on one side and the second 4-bytes emitted on
the other side of the boundary. Therefore we need to align generated
code to 64 bytes and emit a nop whenever the boundary is being crossed
midway (check emit_prefix).

Change-Id: I90e9953089214e15eeef0d70147ea5943fe05f45
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3528993Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Farazmand <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/main@{#79612}