radeon: implement 2D tiling for CIK

Bug fixes and simplification by Marek.
We have to use the tile index of 0 for non-MSAA depth-stencil after all.

Signed-off-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-and-Tested-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>