ALSA: firewire-motu: add a flag for AES/EBU on XLR interface

MOTU Traveler supports AES/EBU on XLR interface and data block of rx/tx
packet includes two chunk for the interface. This commit adds a flag
for this purpose.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>