ALSA: usb-audio: refactor code

Clean up the usb audio driver by factoring out a lot of functions to
separate files. Code for procfs, quirks, urbs, format parsers etc all
got a new home now.

Moved almost all special quirk handling to quirks.c and introduced new
generic functions to handle them, so the exceptions do not pollute the
whole driver.

Renamed usbaudio.c to card.c because this is what it actually does now.
Renamed usbmidi.c to midi.c for namespace clarity.
Removed more things from usbaudio.h.

The non-standard drivers were adopted accordingly.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/proc.h b/sound/usb/proc.h
new file mode 100644
index 0000000..a45b765
--- /dev/null
+++ b/sound/usb/proc.h
@@ -0,0 +1,8 @@
+#ifndef __USBAUDIO_PROC_H
+#define __USBAUDIO_PROC_H
+
+void snd_usb_audio_create_proc(struct snd_usb_audio *chip);
+void snd_usb_proc_pcm_format_add(struct snd_usb_stream *stream);
+
+#endif /* __USBAUDIO_PROC_H */
+