ARM: sun8i: sina33: Enable USB gadget

The micro-USB on the SinA33 has a somewhat interesting design in the sense
that it has a micro USB connector, but the VBUS is (supposed to be)
controlled through an (unpopulated) jumper.

Obviously, that doesn't work really well, and only the peripheral mode
really works. Still enable it.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>