drm/i915/dp: Attach HDR metadata property to DP connector

It attaches HDR metadata property to DP connector on GLK+.
It enables HDR metadata infoframe sdp on GLK+ to be used to send
HDR metadata to DP sink.

v2: Minor style fix

Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190919195311.13972-9-gwan-gyeong.mun@intel.com