[ALSA] snd_usb_caiaq: add support for 'Session I/O' interface

This patch adds suport for Native Instruments new
'Guitar Rig Session I/O' audio hardware.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>