net: netcp: ethss: use rgmii link status for 2u cpsw hardware

Introduce rgmii link status to handle link state events for 2u
cpsw hardware on K2G.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>