drm/i915/dp: s/intel_dp_hdmi_ycbcr420/intel_dp_is_ycbcr420/

intel_dp_hdmi_ycbcr420() does account for native DP 4:2:0
output as well, so lets rename it a bit.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220322120015.28074-5-ville.syrjala@linux.intel.com


Reviewed-by: Uma Shankar <uma.shankar@intel.com>