Added state readout for DP HDR Metadata Infoframe SDP.

v9: Rebased
v10: Rebased
Signed-off-by: NGwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Reviewed-by: NUma Shankar <uma.shankar@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200514060732.3378396-9-gwan-gyeong.mun@intel.com