net: cadence: switch to using nvmem_get_mac_address()

We now have a generalized helper routine to read the MAC address from
nvmem which takes struct device as argument. The nvmem subsystem will
then try device tree first before all other potential providers.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>