device:usb:gadget: android as keyboard gadget

* Comes from here: https://github.com/pelya/android-keyboard-gadget
* Needs this app: https://play.google.com/store/apps/details?id=remote.hid.keyboard.client
* Credits: Sergii Pylypenko and Dmitry Brant

Signed-off-by: Dan Trifan <jimsth@gmail.com>