ASoC: lochnagar: Add device tree binding document

Lochnagar is an evaluation and development board for Cirrus
Logic Smart CODEC and Amp devices. It allows the connection of
most Cirrus Logic devices on mini-cards, as well as allowing
connection of various application processor systems to provide a
full evaluation platform. This driver supports the board
controller chip on the Lochnagar board.
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/cirrus,lochnagar.txt

+Cirrus Logic Lochnagar Audio Development Board
+
+Lochnagar is an evaluation and development board for Cirrus Logic
+Smart CODEC and Amp devices. It allows the connection of most Cirrus
+Logic devices on mini-cards, as well as allowing connection of
+various application processor systems to provide a full evaluation
+platform.  Audio system topology, clocking and power can all be
+controlled through the Lochnagar, allowing the device under test
+to be used in a variety of possible use cases.
+
+This binding document describes the binding for the audio portion
+of the driver.
+
+This binding must be part of the Lochnagar MFD binding:
+  [4] ../mfd/cirrus,lochnagar.txt
+
+Required properties:
+
+  - compatible : One of the following strings:
+                 "cirrus,lochnagar2-soundcard"
+
+  - #sound-dai-cells : Must be set to 1.
+
+  - clocks : Contains an entry for each entry in clock-names.
+  - clock-names : Must include the following clocks:
+      "mclk" Master clock source for the sound card, should normally
+      be set to LOCHNAGAR_SOUNDCARD_MCLK provided by the Lochnagar
+      clock driver.
+
+Example:
+
+lochnagar-sc {
+	compatible = "cirrus,lochnagar2-soundcard";
+
+	#sound-dai-cells = <1>;
+
+	clocks = <&lochnagar_clk LOCHNAGAR_SOUNDCARD_MCLK>;
+	clock-names = "mclk";
+};