drm/i915: Allow an arbitrary number of downclock modes

Remove the "two fixed modes only" limit and grab as many
downclock modes from the EDID as we can find.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220331112822.11462-8-ville.syrjala@linux.intel.com


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