drm/i915/dp: Configure PCON for conversion of output_format to YCbCr444

Handle the case with DP to HDMI PCON, where sink_format is set to YCbCr444.
In that case PCON is required to be configured to convert from given
output_format to YCbCR444.

v2: Drop drm_WARN for invalid case, let MISSING_CASE catch it. (Ville)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230427125605.487769-4-ankit.k.nautiyal@intel.com