drm/i915: Tighten DRRS capability reporting

Only report DRRS capability for the connector if its fixed_modes
list contains at least two modes capable of seamless DRRS switch
between them.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221003113249.16213-6-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>