dts: bindings: pwm: Add Arduino PWM nexus mapping

Add `adruino-header-pwm` map node to describe well Arduino PWM
pin configuration.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>

Author: soburi

dts/bindings/pwm/arduino-header-pwm.yaml

@@ -0,0 +1,14 @@
+# Copyright (C) 2025 TOKITA Hiroshi
+# SPDX-License-Identifier: Apache-2.0
+
+description: |
+  PWM channels exposed on Arduino headers.
+
+  Arduino's PWM pin names shares the same definition as Digital pins one.
+  That is, the mapping of PWM output on pin D3 on Arduino UNO R3 header is
+
+    pwm-map = <9 0 0 &pwm0 1 0 0>;
+
+compatible: "arduino-header-pwm"
+
+include: [base.yaml, pwm-nexus.yaml]

dts/bindings/pwm/pwm-nexus.yaml

@@ -0,0 +1,20 @@
+# Copyright (c) 2025 TOKITA Hiroshi
+# SPDX-License-Identifier: Apache-2.0
+
+# Common fields for PWM nexus nodes
+
+properties:
+  pwm-map:
+    type: compound
+    required: true
+
+  pwm-map-mask:
+    type: array
+
+  pwm-map-pass-thru:
+    type: array
+
+  "#pwm-cells":
+    type: int
+    required: true
+    description: Number of items to expect in a PWM specifier