HID: wiimote: add Nunchuk support

This moves the nunchuk parser over to an extension module. This allows to
make use of hotplugged Nunchuks instead of the old static parser.

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