net: stmmac: Enable mac_managed_pm phylink config

Enable the mac_managed_pm configuration in the phylink_config
structure to avoid the kernel warning during system resume.

Fixes: 744d23c7 ("net: phy: Warn about incorrect mdio_bus_phy_resume() state")
Signed-off-by: Shenwei Wang <shenwei.wang@nxp.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>