USB: android: Add OTG descriptor to configuration

Include OTG descriptor in configuration when gadget is
capable of OTG. SRP and HNP capablities are exposed for now.
This patch will help to inform USB Host that our device
is OTG capable via configuration descriptor.

Change-Id: Idc72ee8168a478f0124c91b99d3123eab5e71adb
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>