Since FallThruTo is often followed by PopControl, we can save a few
cache state copy operations in Liftoff by merging the two.
On epic workloads, this saves ~18% of Steal operations and ~22% of
Split operations.

R=herhut@chromium.org

Bug: v8:8423
Change-Id: I99900eaa49ae14ead6a0c08b69da2175730e077e
Reviewed-on: https://chromium-review.googlesource.com/c/1384093Reviewed-by: Stephan Herhut <herhut@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58420}