net: fec: init MAC prior to mii bus probe

Below case causes mii bus probe failed:
ifconfig eth0 down -> suspend/resume with Mega/fax mix off -> ifconfig eth0 up

In i.MX6SX/i.MX7D chip, Mega/fast mix off feature is supported that means most of
SOC power will be off including ENET MAC for power saving. Once ENET MAC power
off, all initialized MAC registers reset to default, so in the case, it must
init MAC prior to mii bus probe.

Signed-off-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>