usb: device_next: uac2: interface descriptor macros

Add macros to initialize full set of descriptors required for USB Audio
Class 2 instance. Descriptors start with Interface Association
Descriptor that binds together the AudioControl interface and all
AudioStreaming interfaces.

AudioStreaming interfaces have alternate setting 0 without any endpoints
and alternate setting 1 with isochronous endpoint with max packet size
calculated on maximum sample frequency, number of channels, subslot size
and clock synchronization (asynchronous endpoints require +1 sample).

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>