[ALSA] usb audio suspend support

This patch implements suspend/resume support for USB audio devices.
It works with the microphone in my camera.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>