ALSA: dice: Split hwdep functionality into a file

This commit adds a file and move some codes related to hwdep functionality.

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

Additionally, this interface give a way to read Dice notification.

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