USB: gadget: composite: Process GetDescriptor(OTG) request

If gadget is OTG capable, respond to a GetDescriptor(OTG) request
with its OTG descriptor.  This patch adds a utility to function
to find and fill the requested descriptor.

Change-Id: I5b3624b1145d46179b0c4737e82a47c68604cab4
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>