ALSA: usb-audio: add quirk flag to enable native DSD for McIntosh devices

McIntosh devices supporting native DSD require the feature to be
explicitly exposed. Add a flag that fixes an issue where DSD audio was
defaulting to DSD over PCM instead of delivering raw DSD data.

Signed-off-by: Max McCarthy <mmccarthy@mcintoshlabs.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/BL0PR13MB4433226005162D186A8DFF4AD6DFA@BL0PR13MB4433.namprd13.prod.outlook.com


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