ASoC: sunxi: Add bindings for sun8i to SPDIF

The H3 SoC uses the same SPDIF block as found in earlier SoCs, but the
transmit fifo is at a different address.
Signed-off-by: Marcus Cooper <codekipper@gmail.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

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

@@ -10,6 +10,7 @@ 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
+    - "allwinner,sun8i-h3-spdif": for the Allwinner H3 SoC
 
   - reg			: Offset and length of the register set for the device.