dt-bindings: altera: document Arria 5 based board compatibles

Add new compatible for Arria 5 based boards.
Signed-off-by: NKrzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: NDinh Nguyen <dinguyen@kernel.org>

Documentation/devicetree/bindings/arm/altera.yaml

@@ -16,6 +16,8 @@ properties:
     oneOf:
       - description: Arria 5 boards
         items:
+          - enum:
+              - altr,socfpga-arria5-socdk
           - const: altr,socfpga-arria5
           - const: altr,socfpga