These aren't called from or implemented in assembly, thus the exact
registers don't matter. We can remove platform-specific definitions.

This resolves 56 TODOs! ))

Bug: v8:8888
Change-Id: I287fbf7eb3c03d7467ff58a27d614163baf34b3f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2505761Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70875}