dt-bindings: arm: amlogic: add A4 support

Document the new A4 SoC/board device tree bindings.

Amlogic A4 is an application processor designed for smart audio
and IoT applications.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Xianwei Zhao <xianwei.zhao@amlogic.com>
Link: https://lore.kernel.org/r/20240401-basic_dt-v3-1-cb29ae1c16da@amlogic.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>

Author: Xianwei Zhao

Documentation/devicetree/bindings/arm/amlogic.yaml

@@ -202,6 +202,12 @@ properties:
               - amlogic,ad402
           - const: amlogic,a1
 
+      - description: Boards with the Amlogic A4 A113L2 SoC
+        items:
+          - enum:
+              - amlogic,ba400
+          - const: amlogic,a4
+
       - description: Boards with the Amlogic C3 C302X/C308L SoC
         items:
           - enum: