drm/amd/display: Update to using new dccg callbacks

[Why and how]
Update to using new dccg callbacks

Reviewed-by: Chris Park <chris.park@amd.com>
Signed-off-by: Hansen Dsouza <Hansen.Dsouza@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>