drm/amd/display: Add new enable and disable functions

Add new enable and disable functions based on DCCG spec.

Signed-off-by: Hansen Dsouza <Hansen.Dsouza@amd.com>
Reviewed-by: Muhammad Ahmed <ahmed.ahmed@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>