dt-bindings: pinctrl: add binding for Ralink MT7621 pinctrl

Add binding for the Ralink MT7621 pin controller for MT7621 SoC.

Signed-off-by: Arınç ÜNAL <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Acked-by: Sergio Paracuellos <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

Documentation/devicetree/bindings/pinctrl/ralink,mt7621-pinctrl.yaml

···
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/pinctrl/ralink,mt7621-pinctrl.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Ralink MT7621 Pin Controller
+
+maintainers:
+  - Arınç ÜNAL <[e-mail]>
+  - Sergio Paracuellos <[e-mail]>
+
+description:
+  Ralink MT7621 pin controller for MT7621 SoC.
+  The pin controller can only set the muxing of pin groups. Muxing individual
+  pins is not supported. There is no pinconf support.
+
+properties:
+  compatible:
+    const: ralink,mt7621-pinctrl
+
+patternProperties:
+  '-pins$':
+    type: object
+    patternProperties:
+      '^(.*-)?pinmux$':
+        type: object
+        description: node for pinctrl.
+        $ref: pinmux-node.yaml#
+
+        properties:
+          groups:
+            description: The pin group to select.
+            enum: [i2c, jtag, mdio, pcie, rgmii1, rgmii2, sdhci, spi, uart1,
+                   uart2, uart3, wdt]
+
+          function:
+            description: The mux function to select.
+            enum: [gpio, i2c, i2s, jtag, mdio, nand1, nand2, pcie refclk,
+                   pcie rst, pcm, rgmii1, rgmii2, sdhci, spdif2, spdif3, spi,
+                   uart1, uart2, uart3, wdt refclk, wdt rst]
+
+        required:
+          - groups
+          - function
+
+        additionalProperties: false
+
+    additionalProperties: false
+
+allOf:
+  - $ref: "pinctrl.yaml#"
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  # Pinmux controller node
+  - |
+    pinctrl {
+      compatible = "ralink,mt7621-pinctrl";
+
+      i2c_pins: i2c0-pins {
+        pinmux {
+          groups = "i2c";
+          function = "i2c";
+        };
+      };
+    };