ALSA: usb-audio: add native DSD support for XMOS based DACs

Add quirks for XMOS based DACs for native DSD playback support using the new
DSD_U32_LE sample format.

This version adds native DSD support for:
- iFi Audio micro iDSD/nano iDSD (they use the same prod. id)
- DIYINHK USB to I2S/DSD converter

Changes from v2:
- fix and simplify switch statement
Changes from v1:
- use specific product id and alt setting per XMOS based device

[fixed a misc coding style issue by tiwai]

Signed-off-by: Jurgen Kramer <gtmkramer@xs4all.nl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>