Implement instructions for stack operations.
Also, fix some issues that came up after implementing them.

Bug: v8:6600
Change-Id: I83dfe621b123081f9ae4d234605358c9ce81420f
Reviewed-on: https://chromium-review.googlesource.com/956072
Commit-Queue: Sreten Kovacevic <sreten.kovacevic@mips.com>
Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51897}