ASoC: sunxi: Add bindings for sun6i to SPDIF

The A31 SoC uses the same SPDIF block as found in earlier SoCs, but its
reset is controlled via a separate reset controller.
Signed-off-by: Marcus Cooper <codekipper@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/sunxi,sun4i-spdif.txt

@@ -9,6 +9,7 @@ Required properties:
 
   - compatible		: should be one of the following:
     - "allwinner,sun4i-a10-spdif": for the Allwinner A10 SoC
+    - "allwinner,sun6i-a31-spdif": for the Allwinner A31 SoC
 
   - reg			: Offset and length of the register set for the device.
 
@@ -25,6 +26,8 @@ Required properties:
 	"apb"		  clock for the spdif bus.
 	"spdif"		  clock for spdif controller.
 
+  - resets		: reset specifier for the ahb reset (A31 and newer only)
+
 Example:
 
 spdif: spdif@01c21000 {