During MST mode enumeration, if a new dc_sink is created,
populate it with dsc caps as appropriate.

Use drm_dp_mst_dsc_aux_for_port to get the raw caps,
then parse them onto dc_sink with dc_dsc_parse_dsc_dpcd.
Reviewed-by: NWenjing Liu <Wenjing.Liu@amd.com>
Signed-off-by: NDavid Francis <David.Francis@amd.com>
Signed-off-by: NMikita Lipski <mikita.lipski@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>