ARM: dts: sun5i: hsg-h702: Enable USB OTG controller

This tablet has proper USB OTG support, using 3 GPIO pins for
ID and VBUS detection, and also VBUS control.

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