oxfw: add a driver for OXFW970/971 based devices

This commit add a driver for OXFW970/971 based devices. I develop
this driver with Behringer F-Control Audio 202. This device has OXFW970.

There are several issues:
1.ALSA already has firewire-speaker driver which also supports OXFW970/971.
But new driver supports recording equipment. It's the best that merge these
two drivers but new driver is a lack of controls because depending on user-land
control software. What is better?

2.If device doesn't support 'LIST' subfunction of 'EXTENDED STREAM FORMAT
INFORMATION' command defined in 'AV/C Stream Format Information
Specification 1.1 (Apr 2005, 1394TA)', this driver assume its formation of
AMDTP stream is the same as the formation at current sampling rate with
command with 'SINGLE' sunfunction. Is this better?

3.How can this driver get information about current source of clock?

4.FCA 202 transmits AMDTP packet with invalid sequence of SYT value. What is
better for synchronization?