Some 57780 ASIC revision parts do not have NVRAM.  Code the driver so
that it is tolerant of this configuration.
Signed-off-by: NMatt Carlson <mcarlson@broadcom.com>
Signed-off-by: NMichael Chan <mchan@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>