drm/i915/dp: Attach colorspace property

drm/i915/dp: Attach colorspace property

It attaches the colorspace connector property to a DisplayPort connector.
Based on colorspace change, modeset will be triggered to switch to a new
colorspace.

And in order to distinguish colorspace bwtween DP and HDMI connector, it
adds a handling of drm_mode_create_dp_colorspace_property() to
intel_attach_colorspace_property().

Based on colorspace property value create a VSC SDP packet with appropriate
colorspace. This would help to enable wider color gamut like BT2020 on a
sink device.

v9: Addressed review comments from Ville
  - Add a handling of drm_mode_create_dp_colorspace_property() to
    intel_attach_colorspace_property(). This hunk moved from the previous
    commit.

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/20190919195311.13972-6-gwan-gyeong.mun@intel.com