dt-bindings: dwmac: Add bindings for new Ingenic SoCs.

Add the dwmac bindings for the JZ4775 SoC, the X1000 SoC,
the X1600 SoC, the X1830 SoC and the X2000 SoC from Ingenic.

Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>