ALSA: usb-audio: Add support for Denon DN-X1600

ALSA: usb-audio: Add support for Denon DN-X1600

This provides support for Denon DN-X1600 hardware mixer.

The device itself supports 44100, 48000 and 96000 (Hz)
sample rates, but switching rates via software is currently not working.
Therefore, this patch hardcodes the sample rate to 48000Hz which
enables all 8 channels to function correctly when the correct
sample rate is selected on the hardware itself.

MIDI also tested and works.

Signed-off-by: Damien Zammit <damien@zamaudio.com>
Tested-by: xalmoxis@gmail.com
Link: https://lore.kernel.org/r/20210610083528.603942-2-damien@zamaudio.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>