dt-bindings: merge ina209 binding into ina2xx binding

The ina209 binding only differs from other ina2xx bindings in the
compatible string, so add it to the common binding and remove the ina209
binding file.
Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>

Documentation/devicetree/bindings/hwmon/ina209.txt

-ina209 properties
-
-Required properties:
-- compatible: Must be "ti,ina209"
-- reg: I2C address
-
-Optional properties:
-
-- shunt-resistor
-	Shunt resistor value in micro-Ohm
-
-Example:
-
-temp-sensor@4c {
-	compatible = "ti,ina209";
-	reg = <0x4c>;
-	shunt-resistor = <5000>;
-};

Documentation/devicetree/bindings/hwmon/ina2xx.txt

@@ -2,6 +2,7 @@ ina2xx properties
 
 Required properties:
 - compatible: Must be one of the following:
+	- "ti,ina209" for ina209
 	- "ti,ina219" for ina219
 	- "ti,ina220" for ina220
 	- "ti,ina226" for ina226