net: phy: smsc: rename flag energy_enable

Rename the flag to edpd_enable, as we're not enabling energy but
edpd (energy detect power down) mode. In addition change the
type to a bit field member in preparation of adding further flags.

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>