arm64: dts: allwinner: h6: add USB Vbus regulator for Pine H64

The 5V output of the USB ports on Pine H64 is controlled via a GPIO.

Add the USB Vbus regulator device tree node.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Tested-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>