dt-bindings: mmc: owl: Add compatible string for Actions Semi S500 SoC

Add a new compatible string corresponding to the MMC controller found
in the S500 variant of the Actions Semi Owl SoCs family.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
Link: https://lore.kernel.org/r/713f57f4a66fff9a50a8d93643a7987d6560becb.1605823502.git.cristian.ciocaltea@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/owl-mmc.yaml

@@ -17,7 +17,9 @@ properties:
     oneOf:
       - const: actions,owl-mmc
       - items:
-          - const: actions,s700-mmc
+          - enum:
+              - actions,s500-mmc
+              - actions,s700-mmc
           - const: actions,owl-mmc
 
   reg: