HID: wiimote: add support for Guitar-Hero guitars

Apart from drums, Guitar-Hero also ships with guitars. Use the recently
introduced input ABS/BTN-bits to report this to user-space.

Devices are reported as "Nintendo Wii Remote Guitar". If I ever get my
hands on "RockBand" guitars, I will try to report them via the same
interface so user-space does not have to bother which device it deals
with.

Signed-off-by: Nicolas.Adenis-Lamarre <nicolas.adenis.lamarre@gmail.com>
(add commit-msg and adjust to new BTN_* IDs)
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>