ANDROID: usb: gadget: Add Android Accessory Function

USB accessory mode allows users to connect USB host hardware
specifically designed for Android-powered devices. The accessories
must adhere to the Android accessory protocol outlined in the
http://accessories.android.com

 documentation. This allows
Android devices that cannot act as a USB host to still interact with
USB hardware. When an Android device is in USB accessory mode, the
attached Android USB accessory acts as the host, provides power
to the USB bus, and enumerates connected devices.

There are issues (especially with regards to reference counting) which
carry over from prior iterations of this driver, and therefore this
driver should not be used as an example for other development. For these
reasons, this patch is not eligible for android-mainline or future
android16+ branches.

Much of this functionality should be deprecated and removed.

Bug: 120441124
Bug: 317149848
Change-Id: I6b7b6e7b2a348da0d57487e82913de6fe19f2b6e
Signed-off-by: Neill Kapron <nkapron@google.com>