ALSA: firewire-motu: code refactoring to handle model specific switch for protocol v2

In MOTU FireWire series, devices which support protocol version 2 have
several types of hardware design to process audio data frames for isoc
packet. Roughly devices are categorized into three groups:
 - 828mkII
 - Traveler/896HD
 - UltraLite/8pre FireWire

Some bit flags in register addressed by 0x'ffff'f000'0b14
includes device-specific effects.

This commit cleanups implementation of protocol v2 in this point.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20191030080644.1704-6-o-takashi@sakamocchi.jp


Signed-off-by: Takashi Iwai <tiwai@suse.de>