usb: device_next: uac2: Handle speed properties

Generate full and high speed descriptors based on UAC2 instance
properties. Fail the build if an instance does not have speed properties
or if the instance with given speed property exceeds the bandwidth
available at the selected speed.

Remove obsolete no longer used macros to determine offsets inside
complete UAC2 descriptors blob. Only speed-specific descriptors arrays
are supported.

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