dt-bindings: ASoC: xlnx, i2s: Document i2s bindings

Added documentation for I2S IP core DT bindings.
Signed-off-by: Maruthi Srinivas Bayyavarapu <maruthi.srinivas.bayyavarapu@xilinx.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/xlnx,i2s.txt

+Device-Tree bindings for Xilinx I2S PL block
+
+The IP supports I2S based playback/capture audio
+
+Required property:
+ - compatible: "xlnx,i2s-transmitter-1.0" for playback and
+	       "xlnx,i2s-receiver-1.0" for capture
+
+Required property common to both I2S playback and capture:
+ - reg: Base address and size of the IP core instance.
+ - xlnx,dwidth: sample data width. Can be any of 16, 24.
+ - xlnx,num-channels: Number of I2S streams. Can be any of 1, 2, 3, 4.
+		      supported channels = 2 * xlnx,num-channels
+
+Example:
+
+	i2s_receiver@a0080000 {
+		compatible = "xlnx,i2s-receiver-1.0";
+		reg = <0x0 0xa0080000 0x0 0x10000>;
+		xlnx,dwidth = <0x18>;
+		xlnx,num-channels = <1>;
+	};
+	i2s_transmitter@a0090000 {
+		compatible = "xlnx,i2s-transmitter-1.0";
+		reg = <0x0 0xa0090000 0x0 0x10000>;
+		xlnx,dwidth = <0x18>;
+		xlnx,num-channels = <1>;
+	};