net: ethtool: Remove PHYLIB direct dependency

Now that we have introduced ethtool_phy_ops and the PHY library
dynamically registers its operations with that function pointer, we can
remove the direct PHYLIB dependency in favor of using dynamic
operations.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>