fdt: Deprecate "usbethaddr" usage in fdt_fixup_ethernet()

In fdt_fixup_ethernet() only "usbethaddr" is handled to fix up the
first usb ethernet port MAC address. Other additional usb ethernet
ports are ignored as there is no logic to handle "usbeth%daddr".

It is suggested we should use "ethaddr" for all ethernet devices.
Hence deprecate "usbethaddr" usage in fdt_fixup_ethernet().

This actually reverts commit b1f49ab8
"ARM: fdt support: Add usbethaddr as an acceptable MAC".

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
On OMAP4 Panda (+ v4.3 kernel)
Tested-by: Tom Rini <trini@konsulko.com>