fsl/fman: tolerate missing MAC address in device tree

Allow the initialization of the MAC to be performed even if the
device tree does not provide a valid MAC address. Later a random
MAC address should be assigned by the Ethernet driver.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Madalin Bucur <madalin.bucur@oss.nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>