The existing interface assumed that for atomic binop instructions, the
value register and the result register are the same. However, for x64,
this assumption is not always useful, and for platforms like arm, this
assumption is even negative.

The existing interface was originally introduced because ia32 lacks
registers, and we wanted to avoid platform-specific code in
liftoff-compiler.cc. However, by now the lack of registers on ia32
required us to use platform-specific code also in other places, so
we can also use it for atomic binops and thereby enable a better code
generation.

R=clemensb@chromium.org

Bug: v8:10108
Change-Id: If39cc5f49934422b632bb2a5793c7f5d5d2b65c0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2150585Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67173}