etnaviv: implement buffer compression

etnaviv: implement buffer compression

Vivante GPUs have lossless buffer compression using the tile-status bits,
which can reduce memory access and thus improve performance.

This patch only enables compression for "V4" compression GPUs, but the
implementation is tested on GC2000(V1) and GC3000(V2). V1/V2 compresssion
looks absolutely useless, so it is not enabled.

I couldn't test if this patch breaks MSAA, because it looks like MSAA is
already broken.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>