ALSA: usb-audio: Add native DSD support for Mytek DACs

Add new mostly generic code with Mytek VID to support native DSD mode.

This implementation should be easier to maintain when manufacturers
release new products.

Signed-off-by: Jussi Laako <jussi@sonarnerd.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>