doc: dt-bindings: Describe Freescale TSEC ethernet controller

Adapted from the same file name in the kernel device tree bindings
documentation, to use with U-Boot.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

doc/device-tree-bindings/net/fsl-tsec-phy.txt

@@ -0,0 +1,43 @@
+* TSEC-compatible ethernet nodes
+
+Properties:
+
+  - compatible : Should be "fsl,tsec"
+  - reg : Offset and length of the register set for the device
+  - phy-handle : See ethernet.txt file in the same directory.
+  - phy-connection-type : See ethernet.txt file in the same directory. This
+    property is only really needed if the connection is of type "rgmii-id",
+    "rgmii-rxid" and "rgmii-txid" as all other connection types are detected
+    by hardware.
+
+Example:
+	ethernet@24000 {
+		compatible = "fsl,tsec";
+		reg = <0x24000 0x1000>;
+		phy-handle = <&phy0>;
+		phy-connection-type = "sgmii";
+	};
+
+Child nodes of the TSEC controller are typically the individual PHY devices
+connected via the MDIO bus (sometimes the MDIO bus controller is separate).
+
+* MDIO IO device
+
+The MDIO is a bus to which the PHY devices are connected.  For each
+device that exists on this bus, a PHY node should be created.
+
+Required properties:
+  - compatible : Should define the compatible device type for the
+    mdio. Currently supported string/device is "fsl,tsec-mdio".
+  - reg : Offset and length of the register set for the device
+
+Example:
+
+	mdio@24520 {
+		compatible = "fsl,tsec-mdio";
+		reg = <0x24520 0x20>;
+
+		ethernet-phy@0 {
+			reg = <0>;
+		};
+	};