Linux normally has no idea how to retrieve MAC Addresses, but instead
expects the MAC address in the devicetree. This patch adds the MAC
address to the devicetree for Linux if we find a valid one in barebox.
This mechanism is limited of course to devices barebox has a driver for
and which are probed themselves from the devicetree.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>