Abstract some stack slot copies through a macro assembler function. This
eliminates some non-paired stack operations.

Bug: v8:6644
Change-Id: Icaa3ebb1bec42587ad461bd548a4225c7b4e5d15
Reviewed-on: https://chromium-review.googlesource.com/685238Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Cr-Commit-Position: refs/heads/master@{#48177}