dm: sunxi: Add a new config for an FDT-based pcDuino3

For now we won't want to mess with the existing configurations. Create a
new one which will enable device tree and driver model. Note that this
brings the device tree binary into u-boot-sunxi-with-spl.bin.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>