eeepc-wmi: new driver for WMI based hotkeys on Eee PC laptops

Add a WMI driver for Eee PC laptops. Currently it only supports hotkeys.

Signed-off-by: Yong Wang <yong.y.wang@intel.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>
Acked-by: Dmitry Torokhov <dtor@mail.ru>