drm/i915: Split intel_attach_colorspace_property() into HDMI vs. DP variants

With LSPCON we use the AVI infoframe to convey the colorimetry
information (as opposed to DP MSA/SDP), so the property we expose
should match the values we can stuff into the infoframe. Ie. we
must use the HDMI variant of the property, even though we drive
LSPCON in PCON mode. To that end just split
intel_attach_colorspace_property() into HDMI and DP variants
and let the caller worry about which one it wants to use.

Cc: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201130204738.2443-8-uma.shankar@intel.com