ARM: mxs: m28evk: Disable OCOTP OUI loading

Don't load the FEC MAC address from OCOTP, but use the one supplied
via device tree by U-Boot. This is the preferred way, every DT-capable
bootloader does set up "mac-address" and "local-mac-address" properties
into the DT passed to the kernel.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>