PVRTC1 texture dimensions must always be powers of two.
Moreover, Apple hardware requires them to be squares.

Bug: angleproject:5731, angleproject:2634
Change-Id: I5fcdc364b37d17b60cf772c21ba38795272236fd
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2741585Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com>