radeonsi: add DCC decompression (v2)

radeonsi: add DCC decompression (v2)

This is currently not needed but will be necessary when we have
features that do not work with DCC enabled, such as image stores
and sharing non-scanout surfaces.

v2: Marek: rebase, remove decompression from si_flush_resource (not needed)

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>