net: phy: c45: change genphy_c45_ethtool_[get|set]_eee to use EEE linkmode bitmaps

Change genphy_c45_ethtool_[get|set]_eee to use EEE linkmode bitmaps.
This is a prerequisite for adding support for EEE modes beyond bit 31.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>