dt-bindings: net: Add ipq806x mdio bindings

Add documentations for ipq806x mdio driver.
Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/qcom,ipq8064-mdio.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/net/qcom,ipq8064-mdio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Qualcomm ipq806x MDIO bus controller
+
+maintainers:
+  - Ansuel Smith <ansuelsmth@gmail.com>
+
+description:
+  The ipq806x soc have a MDIO dedicated controller that is
+  used to communicate with the gmac phy connected.
+
+allOf:
+  - $ref: "mdio.yaml#"
+
+properties:
+  compatible:
+    const: qcom,ipq8064-mdio
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - "#address-cells"
+  - "#size-cells"
+
+examples:
+  - |
+    #include <dt-bindings/clock/qcom,gcc-ipq806x.h>
+
+    mdio0: mdio@37000000 {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        compatible = "qcom,ipq8064-mdio";
+        reg = <0x37000000 0x200000>;
+
+        clocks = <&gcc GMAC_CORE1_CLK>;
+
+        switch@10 {
+            compatible = "qca,qca8337";
+            /* ... */
+        };
+    };