Add ACPI support for xgmac MDIO bus registration while maintaining
the existing DT support.

The function mdiobus_register() inside of_mdiobus_register(), brings
up all the PHYs on the mdio bus and attach them to the bus.
Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Calvin Johnson <calvin.johnson@oss.nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>