acer-wmi: Add 3G rfkill sysfs file

Add 3G rfkill sysfs file for provide userland to control 3G device
on/off by using WMI method.

Signed-off-by: Lee, Chun-Yi <jlee@novell.com>
Acked-by: Thomas Renninger <trenn@suse.de>
Acked-by: Jiri Benc <jbenc@suse.cz>
Acked-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Carlos Corbaho <carlos@strangeworlds.co.uk>
Cc: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Matthew Garrett <mjg@redhat.com>