The {ParallelRegisterMove} at the end of {AtomicLoad} might need a
temporary scratch register for spilling values to the stack. Make sure
that one is available by giving up the scratch register used for the
address of the atomic access.

R=ahaas@chromium.org

Bug: chromium:1153442
Change-Id: I267c43e2193662c420f96f6683ebd4bbb0e1bca3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2566759Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71564}