HID: wiimote: Add force-feedback support

The wiimote has a single rumble motor. This adds force feedback support for
wiimote devices with FF_RUMBLE. The rumble motor is very simple and only
supports an on/off switch so no complex ff-effects are supported.

This also removes the event callback that was registered before but unused. The
ff-device overwrites this callback, anyway.

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