dell-laptop: Toggle the unsupported hardware killswitch

It is found on Dell Inspiron 1018 that the firmware reports that the hardware
killswitch is not supported. This makes the rfkill key not functional.

This patch forces the driver to toggle the firmware rfkill status in the case
that the hardware killswitch is indicated as unsupported by the firmware.

Signed-off-by: Keng-Yu Lin <keng-yu.lin@canonical.com>
Tested-by: Alessio Igor Bogani <abogani@texware.it>
Signed-off-by: Matthew Garrett <mjg@redhat.com>