The dc_gamma in dc_surface will be programmed to the input
LUT if provided.  If dc_gamma is not provided in dc_surface
regamma may be used to emulate gamma.

Some refactor and cleanup included as well.
Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>