oxfw: Add proc interface for debugging purpose

This commit adds proc interface to get information for debugging.
 - stream formation
 - current sampling rate
oxfw: Add MIDI interface

This commit adds a functionality to capture/playback MIDI messages.

When no AMDTP streams are running, this module starts AMDTP stream at current
sampling rate for MIDI stream.
oxfw: Add PCM interface

This commit adds a functionality to capture/playback PCM samples.

Currently this driver has no functionality to check current source of clock.
When AMDTP stream is already running for PCM, available sampling rate is
limited at current one.
oxfw: Add hwdep interface

This interface is designed for mixer/control application. To use hwdep
interface, the application can get information about firewire node, can
lock/unlock kernel streaming and can get notification at starting/stopping
kernel streaming.