turnip: implement UBWC

This enables UBWC for everything except 3D textures.

It breaks many image_to_image copies but those aren't important and it can
be worked around later (image_to_image copy needs to be done in two steps,
decode from the source format and then encode to the destination format).

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Eric Anholt <eric@anholt.net>