i64x2 mul is more tricky, the algorithm is slightly modified:
- for arm64, we can only use 2 temporaries
- for arm, we only have 1 temporary, so we get another register
manually, if we need it (modify lhs/rhs if they are not used)

Bug: v8:9909
Change-Id: I0398e2c95348a8b49ca9773a78ccfb7af73e2eef
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2128606
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66971}