The temp registers might be needed by the assembler, so avoid using them
in LiftoffAssembler. Use Liftoff cache registers instead. This might
introduce additional spills if all registers are in use, but this is
unlikely.

This also simplifies the logic to ensure non-aliasing of certain
registers.

R=ahaas@chromium.org

Bug: chromium:922933, v8:6600
Change-Id: Ie929d9de0b6f4f41c6117d820b6a367dd0a342f7
Reviewed-on: https://chromium-review.googlesource.com/c/1424862Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58961}