net: ethernet: fec: Revert "net: ethernet: fec: Replace interrupt driven MDIO with polled IO"

This reverts commit 29ae6bd1

.

The commit breaks ethernet function on i.MX6SX, i.MX7D, i.MX8MM,
i.MX8MQ, and i.MX8QXP platforms. Boot yocto system by NFS mounting
rootfs will be failed with the commit.

Signed-off-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>