Instructions ins and ext didn't work properly when size = 32 because of
incorrect mask initialization, this CL fixes this. A test for Ins is
also added.

BUG=

Change-Id: I95cc8e13aaa2341b34ae59dae1eefb64c551b8b4
Reviewed-on: https://chromium-review.googlesource.com/558872
Commit-Queue: Miran Karić <Miran.Karic@imgtec.com>
Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@imgtec.com>
Cr-Commit-Position: refs/heads/master@{#46378}