net: phy: Register ethtool PHY operations

Utilize ethtool_set_ethtool_phy_ops to register a suitable set of PHY
ethtool operations in a dynamic fashion such that ethtool will no longer
directy reference PHY library symbols.

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