dt-bindings: net: add schema for ASIX USB Ethernet controllers

Create schema for ASIX USB Ethernet controllers and import some of
currently supported USB IDs form drivers/net/usb/asix_devices.c

These devices are already used in some of DTs. So, this schema makes it official.
NOTE: there was no previously documented txt based DT binding for this
controllers.
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220517111505.929722-2-o.rempel@pengutronix.de

Documentation/devicetree/bindings/net/asix,ax88178.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/net/asix,ax88178.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: The device tree bindings for the USB Ethernet controllers
+
+maintainers:
+  - Oleksij Rempel <o.rempel@pengutronix.de>
+
+description: |
+  Device tree properties for hard wired USB Ethernet devices.
+
+allOf:
+  - $ref: ethernet-controller.yaml#
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - usbb95,1720   # ASIX AX88172
+          - usbb95,172a   # ASIX AX88172A
+          - usbb95,1780   # ASIX AX88178
+          - usbb95,7720   # ASIX AX88772
+          - usbb95,772a   # ASIX AX88772A
+          - usbb95,772b   # ASIX AX88772B
+          - usbb95,7e2b   # ASIX AX88772B
+
+  reg: true
+  local-mac-address: true
+  mac-address: true
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    usb {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        ethernet@1 {
+            compatible = "usbb95,7e2b";
+            reg = <1>;
+            local-mac-address = [00 00 00 00 00 00];
+        };
+    };
+  - |
+    usb {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        usb1@1 {
+            compatible = "usb1234,5678";
+            reg = <1>;
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            ethernet@1 {
+               compatible = "usbb95,772b";
+               reg = <1>;
+            };
+        };
+    };