ARM: dtsi: sunxi: add common VBUS regulator

Until now the regulator nodes for powering USB VBUS
existed only for the two host controllers. Now the regulator
is added for USB OTG too.

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