drm/amd/display: add support for chroma offset

[Why]
Adding support for chroma subsampling offset (cositing) in scaler
calculations to adjust reference point where we determine post-scaling
chroma value in YUV420 surfaces.

[How]
Add support for cositing options: NONE, LEFT and TOPLEFT Add debug
option force_cositing and set default to TOPLEFT to maintain same
behaviour as without offset support.

Reviewed-by: Jun Lei <jun.lei@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Samson Tam <samson.tam@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>