acer-wmi: Add rfkill support for wireless and bluetooth

This patch implements rfkill support for the wireless and bluetooth devices
commonly found on Acer laptops.

For now, we will always poll these devices once a second to guarantee we
can catch state changes. On newer Acer laptops, it may be possible to rely
on WMI events to do this instead, and experimental support for this will be
added in a later patch.

3G has been deliberately left off for now, as we still have no way to
detect it, (nor, AFAIK, has any Linux user tried the code) and on laptops
that don't support 3G, trying to poll for the status will leave the logs
full of ACPI tracebacks.

The old sysfs interface for wireless and bluetooth will be removed in a
later patch.

(Thanks to Henrique de Moraes Holschuh and Dmitry Torokhov for reviewing
this patch).

Signed-off-by: Carlos Corbacho <carlos@strangeworlds.co.uk>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>