freedreno/a3xx: add fake RGTC support (required for GL3)

freedreno/a3xx: add fake RGTC support (required for GL3)

Also throw in LATC while we're at it (same exact format). This could be
made more efficient by keeping a shadow compressed texture to use for
returning at map time. However... it's not worth it for now...
presumably compressed textures are not updated often.

Lastly fix up Z32S8 transfers to non-0 layers.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Rob Clark <robclark@freedesktop.org>