hwmon: (ltq-cputemp) add devicetree bindings documentation

Document the devicetree bindings for the ltq-cputemp

Signed-off-by: Florian Eckert <[e-mail]>
Signed-off-by: Guenter Roeck <[e-mail]>

Documentation/devicetree/bindings/hwmon/ltq-cputemp.txt

···
+Lantiq cpu temperatur sensor
+
+Requires node properties:
+- compatible value :
+	"lantiq,cputemp"
+
+Example:
+	cputemp@0 {
+		compatible = "lantiq,cputemp";
+	};