USB: f_audio_source: Add superspeed support

Add required superspeed descriptors for audio_source driver
to work in superspeed mode, which is missing currently.

Change-Id: I4e2cf69a9fd75c354b6505168eecb1aede606b88
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>