RFKILL: allow one to specify led trigger name

Allow the rfkill driver to specify led trigger name.
By default it still defaults to the name of rfkill switch.

Signed-off-by: Dmitry Baryshkov <dbaryshkov@gmail.com>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>