ASoC: dt-bindings: add schema for WM8961

Create a simple DT schema for the existing Wolfson WM8961 driver so that
DT support can be added to the driver.
Signed-off-by: Doug Brown <doug@schmorgal.com>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221003032414.248326-2-doug@schmorgal.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/wlf,wm8961.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/wlf,wm8961.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Wolfson WM8961 Ultra-Low Power Stereo CODEC
+
+maintainers:
+  - patches@opensource.cirrus.com
+
+properties:
+  compatible:
+    const: wlf,wm8961
+
+  reg:
+    maxItems: 1
+
+  '#sound-dai-cells':
+    const: 0
+
+required:
+  - compatible
+  - reg
+  - '#sound-dai-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+          #address-cells = <1>;
+          #size-cells = <0>;
+
+          wm8961: codec@4a {
+                  compatible = "wlf,wm8961";
+                  reg = <0x4a>;
+                  #sound-dai-cells = <0>;
+          };
+    };