This adds support for reading the EEPROM which has a "NXID" data
structure on it. The MAC addresses for the ethernet devices are
found here which are registered with this patch.

The NXID data structure is also found on other NXP Layerscape boards,
so once we support other boards the code should be moved somewhere
where it can be shared between boards.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>