ANDROID: usb: gadget: Add support for MTP OS desc

ANDROID: usb: gadget: Add support for MTP OS desc

Windows requires OS specific descriptors for automatic
install of drivers for MTP devices.

https://msdn.microsoft.com/en-us/library/windows/
hardware/gg463179.aspx

BUG=24583401
BUG=chrome-os-partner:43409

Change-Id: I9397072ca3d183efbc9571c6cde3790f10d8851e
Signed-off-by: Badhri Jagan Sridharan <Badhri@google.com>
Reviewed-on: https://chromium-review.googlesource.com/304346
Commit-Ready: Andrew Bresticker <abrestic@chromium.org>
Tested-by: Andrew Bresticker <abrestic@chromium.org>
Reviewed-by: Andrew Bresticker <abrestic@chromium.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>