ARM: dts: sun6i: hummingbird: Enable USB OTG

The A31 Hummingbird has a mini USB OTG port, and uses GPIO pins from the
SoC for ID pin and VBUS detection and VBUS control. The PMIC can also do
VBUS detection and control.

Here we prefer to use the PMIC's DRIVEVBUS function to control VBUS for
USB OTG, as that is the hardware default.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>