drm/amd/display: create new function prototype update_dchub for dcn

dcn version of update_dchub now uses hubbub instead of hwseq

Signed-off-by: Yue Hin Lau <Yuehin.Lau@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>