drm/amd/display: Refactoring DSC enum dsc_bits_per_comp.

[Why]
Previously the 'dsc_bits_per_comp' enumeration was defined in individual
.c files, making it unavailable for other files that may need it.

[How]
The 'dsc_bits_per_comp' enumeration has been relocated to a common header
file.

Reviewed-by: Mounika Adhuri <Mounika.Adhuri@amd.com>
Reviewed-by: Martin Leung <martin.leung@amd.com>
Signed-off-by: Bhuvanachandra Pinninti <bpinnint@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>