In {Assembler::and_} we might need to use the scratch register. Thus use
a free LiftoffRegister instead to emit i32 popcnt.

R=ahaas@chromium.org
CC=george.wort@arm.com

Bug: chromium:918284
Change-Id: Ia814899bf6e33dd4989fd09329542b4bc09b48df
Reviewed-on: https://chromium-review.googlesource.com/c/1405036Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58723}