net: stmmac: dwmac-rk: Add handling for RGMII_ID/RXID/TXID

ATM dwmac-rk will always set and enable it's internal delay lines.
Using PHY internal delays in combination with the phy-mode
rgmii-id/rxid/txid was not possible. Only rgmii was supported.

Now we can disable rockchip's gmac delay lines and also use
rgmii-id/rxid/txid.

Tested only with a RK3288 based board.

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>
Signed-off-by: David S. Miller <davem@davemloft.net>