ALSA: usb-audio: Add basic capture support for Pioneer DJ DJM-250MK2

This patch extends support for DJM-250MK2 and allows recording.
However, DVS is not possible yet (see the comment in code).

Signed-off-by: František Kučera <franta-linux@frantovo.cz>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200825153113.6352-1-konference@frantovo.cz


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