Every JS function has a bailout check at the beginning which makes sure it was
not lazily deoptimized. We can improve the check slightly:

- Load the code data container directly with a pc-relative load instead of
  ADR+LDR.
- Check the deoptimization bit with TBZ directly, saving us a TST instruction.
- Use one of the macro-assembler's dedicated scratch registers instead of x2.

Bug: 
Change-Id: Iea4824c74ed5a01b18595d5e980788f9745bbb6e
Reviewed-on: https://chromium-review.googlesource.com/864446Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Pierre Langlois <pierre.langlois@arm.com>
Cr-Commit-Position: refs/heads/master@{#50570}