drm/i915: Combine the EDID fixed_mode+downclock_mode lookup into one

drm/i915: Combine the EDID fixed_mode+downclock_mode lookup into one

The intel_panel_add_edid_fixed_mode() vs.
intel_panel_add_edid_downclock_mode() split is not really
helpful. Let's just roll those into a single function so
that the connector init code doesn't have to care too much
about this. All we need to know is whether DRRS should be
allowed or not.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220331112822.11462-6-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>