drm/amd/display: support CP2520 pattern 2 for HBR2 compliance

- also some clean up

Signed-off-by: Tony Cheng <tony.cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>