HID: wiimote: convert ACCEL to module

Accelerometer data is very similar to KEYS handling. Therefore, convert
all ACCEL related handling into a sub-device module similar to KEYS.

This doesn't change any semantics but only moves code over to
wiimote-modules.

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