HID: wiimote: Register led class devices

This registers 4 led devices to allow controlling the wiimote leds via standard
LED sysfs API. It removes the four sysfs attributes so we don't have two APIs
for one device.

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