usb: gadget: f_uac2: Expose all string descriptors through configfs.

usb: gadget: f_uac2: Expose all string descriptors through configfs.

This makes all string descriptors configurable for the UAC2 gadget
so the user can configure names of terminals and controls. Alt mode
names are not included for now and will be in future work related
to adding alternate settings.

discussion thread for api changes for alt mode settings:
https://lore.kernel.org/linux-usb/35be4668-58d3-894a-72cf-de1afaacae45@ivitera.com/T/

Signed-off-by: Chris Wulff <chris.wulff@biamp.com>
Link: https://lore.kernel.org/r/20240804001923.3279431-2-crwulff@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>