This patch adds RFKill handler functions to the driver, allowing it
to register and update the rfkill switch status.

Also, a comment block was moved from the header to the poll function,
as it explains why we need to poll the killswitch on older devices.
Signed-off-by: Azael Avalos <coproscefalo@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>