net: phy: smsc: add helper smsc_phy_config_edpd

Add helper smsc_phy_config_edpd() and explicitly clear bit
MII_LAN83C185_EDPWRDOWN is edpd_enable isn't set.
Boot loader may have left whatever value.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>