drm: Sort connector modes based on vrefresh

Keeping the modes sorted by vrefresh before the pixel clock makes the
mode list somehow more pleasing to the eye.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>