ALSA: usb-audio: add the initial mix for Presonus Studio 1824c

ALSA: usb-audio: add the initial mix for Presonus Studio 1824c

A reasonable initial mix for the 1824c is the one that
Presonus Universal Control calls bypass.
It mutes all the physical inputs, and connects
Daw channel 1 to Line out channel 1 (left)
Daw channel 2 to Line out channel 2 (right)
Daw channel 3 to Line out channel 3 (left)
etc.

To get the most out of the 1824c a mixer application like
Universal Control is needed. One is available for linux
Link: https://github.com/royvegard/baton
Signed-off-by: Roy Vegard Ovesen <roy.vegard.ovesen@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>