This implementation uses mutex to implement those instructions.
I will add 32-bit version LL/SC after review.

Change-Id: I7b0e2b42527bc21060a84eb5e27099e129f2858f
Reviewed-on: https://chromium-review.googlesource.com/c/1354462Reviewed-by: Sreten Kovacevic <skovacevic@wavecomp.com>
Commit-Queue: Predrag Rudic <prudic@wavecomp.com>
Cr-Commit-Position: refs/heads/master@{#58048}