ALSA: usb-audio: scarlett2: Add "Sync Status" control

Add "Sync Status" control to display the sync locked/unlocked status.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/d6967d7a34b2ea7e0672ba819e4ed8b99e8dcd35.1624294591.git.g@b4.vu


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