ALSA: usb-audio: Add DSD support for EVGA NU Audio

EVGA NU Audio is actually a USB audio device on a PCIexpress card,
with it's own USB controller. It supports both PCM and DSD.

Signed-off-by: Jussi Laako <jussi@sonarnerd.net>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20190924071143.30911-1-jussi@sonarnerd.net


Signed-off-by: Takashi Iwai <tiwai@suse.de>