Allwinner SoCs typically have a Mentor Graphics Inventra MUSB high speed
dual role controller for USB OTG.

Now that the issue with MUSB and USB gadget registration order has been
resolved, we can enable this driver in dual role mode.

This patch only enables the driver core and Allwinner platform support.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>