This patch adds initial support for the Behringer BCD2000 USB DJ controller.
At the moment, only the MIDI part of the device is working, i.e. knobs,
buttons and LEDs.

I also plan to add support for the audio part, but I assume that this will
require more effort than the rather simple MIDI interface. Progress can be
tracked at https://github.com/anyc/snd-usb-bcd2000.

Signed-off-by: Mario Kicherer
Reviewed-by: Daniel Mack
Reviewed-by: Clemens Ladisch
Signed-off-by: Takashi Iwai