net: stmmac: allow stmmac to probe for C45 PHY devices

Assign stmmac's mdio_bus probe capabilities to MDIOBUS_C22_C45.
This extended the probing of C45 PHY devices on the MDIO bus.

Signed-off-by: Wong Vee Khee <vee.khee.wong@intel.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>