dt-bindings: mips: Add support for RTL83xx SoC series

Signed-off-by: Bert Vermeulen <bert@biot.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Documentation/devicetree/bindings/mips/realtek-rtl.yaml

+# SPDX-License-Identifier: GPL-2.0-or-later OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mips/realtek-rtl.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Realtek RTL83xx/93xx SoC series device tree bindings
+
+maintainers:
+  - Bert Vermeulen <bert@biot.com>
+  - Sander Vanheule <sander@svanheule.net>
+
+properties:
+  $nodename:
+    const: "/"
+  compatible:
+    oneOf:
+      # RTL8382-based boards
+      - items:
+          - enum:
+              - cisco,sg220-26
+          - const: realtek,rtl8382-soc
+
+additionalProperties: true