drivers: net: fsl-mc: Fixup MAC addresses in DPC

Fixup port_mac_address property in MC DPC with values from the u-boot
environment. Since u-boot already reads the environment MAC addresses
when probing the PHYs, use these values.

The u-boot environment MAC addresses take precedence over any eventual
ones defined in the DPC, except for the case where they are randomly
assigned (no u-boot env value declared for port).

The patch assumes the "/board_info/ports/" node is present in the DPC.

Signed-off-by: Bogdan Purcareata <bogdan.purcareata@nxp.com>
Reviewed-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
[York S: Fix several indentations]
Reviewed-by: York Sun <york.sun@nxp.com>