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>

sound/usb/quirks.c

@@ -1174,5 +1174,21 @@ u64 snd_usb_interface_dsd_format_quirks(struct snd_usb_audio *chip,
 		}
 	}
 
+	/* XMOS based USB DACs */
+	switch (chip->usb_id) {
+	/* iFi Audio micro/nano iDSD */
+	case USB_ID(0x20b1, 0x3008):
+		if (fp->altsetting == 2)
+			return SNDRV_PCM_FMTBIT_DSD_U32_LE;
+		break;
+	/* DIYINHK DSD DXD 384kHz USB to I2S/DSD */
+	case USB_ID(0x20b1, 0x2009):
+		if (fp->altsetting == 3)
+			return SNDRV_PCM_FMTBIT_DSD_U32_LE;
+		break;
+	default:
+		break;
+	}
+
 	return 0;
 }