ALSA: fireface: add skeleton for RME Fireface series

This commit adds a new driver for RME Fireface series. This commit just
creates/removes card instance according to IEEE 1394 bus event. More
functions will be added in following commits.

Three types of firmware have released by RME GmbH; for Fireface 400, for
Fireface 800 and for UCX/802/UFX. It's reasonable that these models use
different protocol for communication. Currently, I've investigated
Fireface 400 and nothing others.

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