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

Add a new compatible string corresponding to the DMA controller found
in the S500 variant of the Actions Semi Owl SoCs family. Additionally,
order the entries alphabetically.
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/2bd23ef5dad5dd613006c20d714b1be3c4d38e7a.1609263738.git.cristian.ciocaltea@gmail.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

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

@@ -8,8 +8,8 @@ title: Actions Semi Owl SoCs DMA controller
 
 description: |
   The OWL DMA is a general-purpose direct memory access controller capable of
-  supporting 10 and 12 independent DMA channels for S700 and S900 SoCs
-  respectively.
+  supporting 10 independent DMA channels for the Actions Semi S700 SoC and 12
+  independent DMA channels for the S500 and S900 SoC variants.
 
 maintainers:
   - Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
@@ -20,8 +20,9 @@ allOf:
 properties:
   compatible:
     enum:
-      - actions,s900-dma
+      - actions,s500-dma
       - actions,s700-dma
+      - actions,s900-dma
 
   reg:
     maxItems: 1