ALSA: usb-audio: Add DSD support for Comtrue USB Audio device

The vendor Comtrue Inc. (0x2fc6) produces USB audio chipsets like
the CT7601 which are capable of Native DSD playback.

This patch adds QUIRK_FLAG_DSD_RAW for Comtrue (VID 0x2fc6), which enables
native DSD playback (DSD_U32_LE) on their USB Audio device. This has been
verified under Ubuntu 25.04 with JRiver.

Signed-off-by: noble.yang <noble.yang@comtrue-inc.com>
Link: https://patch.msgid.link/20250731110614.4070-1-noble228@gmail.com


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