dt-bindings: arm: Add Akebi96 board support

Add uniphier-ld20-akebi96 compatible string for
Akebi96 board support.
Signed-off-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>

Documentation/devicetree/bindings/arm/socionext/uniphier.yaml

@@ -51,6 +51,7 @@ properties:
       - description: LD20 SoC boards
         items:
           - enum:
+            - socionext,uniphier-ld20-akebi96
             - socionext,uniphier-ld20-global
             - socionext,uniphier-ld20-ref
           - const: socionext,uniphier-ld20