hwmon: 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>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/devicetree/bindings/hwmon/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 hardware monitor
+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-hwmon"
+
+Example:
+
+lochnagar-hwmon {
+	compatible = "cirrus,lochnagar2-hwmon";
+};