Implement open() and close() methods for the input device so that we
do not start the device unless there are users listening to the events.
Acked-by: NChris Bagwell <chris@cnpbagwell.com>
Tested-by: NPing Cheng <pingc@wacom.com>
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>