sunxi: H616: enable USB support for H616 boards

Now that the PHY driver supports the H616 USB PHY, we can enable USB
support for the two H616 boards.
As the OrangePi Zero2 has a USB-C port hard-wired to peripheral mode,
let's enable USB gadget mode for port 0, so people can use fastboot,
ethernet or mass storage functionality.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>