ARM: dts: sun5i: q8-common: Enable USB power supply

On the A13 Q8 tablets, the PMIC's USB power supply (VBUS) is connected
to the external OTG port. This can be used to provide power and OTG VBUS
sensing.

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