libusbg: schemes: Allow to export midi function
libusbg: schemes: Allow to export midi function

Add support for exporting midi function to gadget scheme.

Signed-off-by: Pawel Szewczyk <1691dcf8dab804b326e5e4b9ab228a1c3b23a2f2@samsung.com>
Reviewed-by: Krzysztof Opasiak <8064eda6f94b3817252b7d7649cf754592f63500@samsung.com>

pszewczyk/libusbg,pszewczyk/libusbg