Qemu adds 'virtio,mmio' nodes to the device tree. Before passing it to the
bootloader or the Linux kernel. This fixup handler copies these nodes to
the new device tree.

Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>
Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>