dt-bindings: bus: add palmbus device tree bindings

Add device tree bindings for palmbus controller present in all the MIPS
ralink based SoCs.
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20211016203323.9165-1-sergio.paracuellos@gmail.comSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/bus/palmbus.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/bus/palmbus.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Ralink PalmBus Device Tree Bindings
+
+maintainers:
+  - Sergio Paracuellos <sergio.paracuellos@gmail.com>
+
+description: |
+  The ralink palmbus controller can be found in all ralink MIPS
+  SoCs. It provides an external bus for connecting multiple
+  external devices to the SoC.
+
+properties:
+  $nodename:
+    pattern: "^palmbus(@[0-9a-f]+)?$"
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 1
+
+  compatible:
+    const: palmbus
+
+  reg:
+    maxItems: 1
+
+  ranges: true
+
+patternProperties:
+  # All other properties should be child nodes with unit-address and 'reg'
+  "@[0-9a-f]+$":
+    type: object
+    properties:
+      reg:
+        maxItems: 1
+
+    required:
+      - reg
+
+required:
+  - compatible
+  - reg
+  - "#address-cells"
+  - "#size-cells"
+  - ranges
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/mips-gic.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+    palmbus@1e000000 {
+        compatible = "palmbus";
+        reg = <0x1e000000 0x100000>;
+        #address-cells = <1>;
+        #size-cells = <1>;
+        ranges = <0x0 0x1e000000 0x0fffff>;
+
+        gpio@600 {
+            #gpio-cells = <2>;
+            #interrupt-cells = <2>;
+            compatible = "mediatek,mt7621-gpio";
+            gpio-controller;
+            gpio-ranges = <&pinctrl 0 0 95>;
+            interrupt-controller;
+            reg = <0x600 0x100>;
+            interrupt-parent = <&gic>;
+            interrupts = <GIC_SHARED 12 IRQ_TYPE_LEVEL_HIGH>;
+        };
+    };
+
+...