Add RGMII to RGMII direct connection support

rolandash

The kernel device tree needs to be modified in order to support RGMII to RGMII direct connection.

make sure 'fec1' node is enabled in device tree
make sure phy-mode is changed to
```
phy-mode = "rgmii-id";
```

add following section in 'fec1' node

    fixed-link {
        speed = <1000>;
        full-duplex;
    };

RGMII internal delay needs to be set for TXC on the peer.

rolandash

Note that TXC and RXC is enough for RGMII direct connection. ETH_REF_CLK is not mandatory in terms of RGMII link, unless the chip itself needs a source of clock input.