dt-bindings: arm: zte: Add D-Link DWR932M board based on zx297520v3 SoC

This adds a new binding file for ZTE, containing their zx297520v3 SoC
and one board (D-Link DWR-932M) based on it.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Stefan Dösinger <stefandoesinger@gmail.com>
---

Changelog:

v6:
Removed extra boards, I'll add them when submitting their individual
DTS files. Rephrase the subject to add "zte" and remove the redundant
use of "binding".

Moved the devicetree bindings patch ahead of the implementation patches.

Moved the MAINTAINERS section from "ZX29" to "ARM/ZTE".

Documentation/devicetree/bindings/arm/zte.yaml

@@ -0,0 +1,26 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/arm/zte.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ZTE zx platforms
+
+maintainers:
+  - Stefan Dösinger <stefandoesinger@gmail.com>
+
+description: |
+  ARM platforms using SoCs designed by ZTE. Currently this supports devices
+  based on the zx297520v3 SoC which is found in LTE routers.
+
+properties:
+  $nodename:
+    const: "/"
+  compatible:
+    oneOf:
+      - items:
+          - enum:
+              - dlink,dwr932m
+          - const: zte,zx297520v3
+
+additionalProperties: true