cxgb3: simplify port type struct and usage

Second step in overall phy layer reorganization.
Clean up the port_type_info structure.
Support coextistence of clause 22 and clause 45 MDIO devices.
Select the type of MDIO transaction on a per transaction basis.

Signed-off-by: Divy Le Ray <divy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>