[arm64] Align stack ops in the arm64 deoptimizer

Align the stack operations in the deoptimizer and take the opportunity to
factorise and improve the code generated for copying.

Bug: v8:6644
Change-Id: I854a975c371936bbf720d56e80dc0c9d68fe7c92
Reviewed-on: https://chromium-review.googlesource.com/763535Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Cr-Commit-Position: refs/heads/master@{#49420}