drivers: net: xgene: fix new firmware backward compatibility with older driver

This patch fixes the backward compatibile of the older driver with the
newer firmware by making the binding unique so that the older driver won't
recognize the non-supported interfaces.

Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: Keyur Chudgar <kchudgar@apm.com>
Tested-by: Mark Langsdorf <mlangsdo@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>