ALSA: firewire-motu: add a flag for chunks for main 1/2 out

This driver explicitly assumes that all of supported models have main data
chunk separated from chunk for analog ports. However, MOTU Traveler doesn't
support the separated main data chunk.

This commit adds a flag for the separated main data chunk.

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