ALSA: usb-audio: Add Pioneer DJ/AlphaTheta DJM-A9 Mixer

This also includes a change to the capture level as they differ with
this device, as well as additional values for prefader channels.

Acked-by: Olivia Mackintosh <livvy@base.nu>
Signed-off-by: Sarah Grant <s@srd.tw>
Link: https://patch.msgid.link/20241025163927.12662-1-s@srd.tw


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