sunxi: H616: OrangePi Zero 2: enable USB power supply

The OrangePi Zero 2 has a USB VBUS regulator, controlled by pin PC16.
This is correctly described in the DT, but the patches for supporting
this are still pending.

Meanwhile add our good old CONFIG_USB1_VBUS_PIN to the defconfig file,
to enable power on the USB port and allow using a USB flash drive, for
instance.

Fixes: 6acc5fa5 ("sunxi: H616: enable USB support for H616 boards")
Reported-by: Mikhail Kalashnikov <iuncuim@gmail.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>