drm/i915: Pass connector state to pfit calculations

Pass the entire connector state to intel_{gmch,pch}_panel_fitting().
For now we just need to get at .scaling_mode but in the future we'll
want access to the margin properties as well.

v2: Deal with intel_dp_ycbcr420_config()

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200422161917.17389-5-ville.syrjala@linux.intel.com
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>