dt-bindings: dma: altera-msgdma: make response port optional

Response port is not required in some configuration of the IP core.
Signed-off-by: NOlivier Dautricourt <olivier.dautricourt@orolia.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Reviewed-by: NStefan Roese <sr@denx.de>
Link: https://lore.kernel.org/r/fb28146a23a182be9e5435c1d3e5cac36b372294.1623898678.git.olivier.dautricourt@orolia.comSigned-off-by: NVinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/dma/altr,msgdma.yaml

@@ -24,13 +24,15 @@ properties:
     items:
       - description: Control and Status Register Slave Port
       - description: Descriptor Slave Port
-      - description: Response Slave Port
+      - description: Response Slave Port (Optional)
+    minItems: 2
 
   reg-names:
     items:
       - const: csr
       - const: desc
       - const: resp
+    minItems: 2
 
   interrupts:
     maxItems: 1