dt-bindings: arm: airoha: Add binding for EN7523 SoC and EVB

Add devicetree binding for Airoha EN7523 SoC and evaluation board.
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NJohn Crispin <john@phrozen.org>
Signed-off-by: NBert Vermeulen <bert@biot.com>
Signed-off-by: NFelix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20211220211854.89452-3-nbd@nbd.nameSigned-off-by: NMatthias Brugger <matthias.bgg@gmail.com>

Documentation/devicetree/bindings/arm/airoha.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/arm/airoha.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Airoha SoC based Platforms Device Tree Bindings
+
+maintainers:
+  - Felix Fietkau <nbd@nbd.name>
+  - John Crispin <john@phrozen.org>
+
+description:
+  Boards with an Airoha SoC shall have the following properties.
+
+properties:
+  $nodename:
+    const: '/'
+  compatible:
+    oneOf:
+      - items:
+          - enum:
+              - airoha,en7523-evb
+          - const: airoha,en7523
+
+additionalProperties: true
+
+...