dell-laptop: Only enable rfkill functionality on laptops with a hw killswitch

All my testing has been on laptops with a hw killswitch, so to be on the
safe side disable rfkill functionality on models without a hw killswitch for
now. Once we gather some feedback on laptops without a hw killswitch this
decision maybe reconsidered.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>