asus-laptop: control how BLED and WLED should be exposed

Let the user tells if BLED and WLED should be exposed as led or
rfkill (the old sysfs are still here, but this adds a standard
interface to control the device).

For example on my A6JC, with WAPF=1, I would do:

$ modprobe asus-laptop wled_type=led bluetooth_type=rfkill

There is still no known way to automatically guess what BLED
and WLED methods will control, it's why user information is needed.

A userspace database could do that automatically, and maybe some DMI
matching in the driver.

Signed-off-by: Corentin Chary <corentin.chary@gmail.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>