HID: wiimote: Add accelerometer input device

Add new input device for every wiimote which is used to report accelerometer
data to userspace. Only if the input device is currently open, we make the
wiimote send accelerometer data. This saves a whole lot of energy on the wiimote
if an application is only interested in button input reports.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>