Using x16/x17 for tail calls allows us to use a "BTI c" instead
of "BTI jc" landing pad. This means that we cannot enter functions
with a jump to a register other than x16/x17 anymore.

Bug: v8:10026
Change-Id: If5af1af861acc19f9e0dfc19c38d6a57a6fb6b6d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2276049Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Cr-Commit-Position: refs/heads/master@{#68655}