dt-bindings: interrupt-controller: Add Realtek RTL838x/RTL839x support

Document the binding for the Realtek RTL838x/RTL839x interrupt controller.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bert Vermeulen <bert@biot.com>
[maz: Add a commit message, as the author couldn't be bothered...]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210122204224.509124-2-bert@biot.com

Documentation/devicetree/bindings/interrupt-controller/realtek,rtl-intc.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/interrupt-controller/realtek,rtl-intc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Realtek RTL SoC interrupt controller devicetree bindings
+
+maintainers:
+  - Birger Koblitz <mail@birger-koblitz.de>
+  - Bert Vermeulen <bert@biot.com>
+  - John Crispin <john@phrozen.org>
+
+properties:
+  compatible:
+    const: realtek,rtl-intc
+
+  "#interrupt-cells":
+    const: 1
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  interrupt-controller: true
+
+  "#address-cells":
+    const: 0
+
+  interrupt-map:
+    description: Describes mapping from SoC interrupts to CPU interrupts
+
+required:
+  - compatible
+  - reg
+  - "#interrupt-cells"
+  - interrupt-controller
+  - "#address-cells"
+  - interrupt-map
+
+additionalProperties: false
+
+examples:
+  - |
+    intc: interrupt-controller@3000 {
+      compatible = "realtek,rtl-intc";
+      #interrupt-cells = <1>;
+      interrupt-controller;
+      reg = <0x3000 0x20>;
+      #address-cells = <0>;
+      interrupt-map =
+              <31 &cpuintc 2>,
+              <30 &cpuintc 1>,
+              <29 &cpuintc 5>;
+    };