device-tree: bindings: max17042_battery: add all of the compatible strings

The bindings are missing documentation for some of the compatible
strings.
Signed-off-by: Angus Ainslie (Purism) <angus@akkea.ca>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Documentation/devicetree/bindings/power/supply/max17042_battery.txt

@@ -2,7 +2,11 @@ max17042_battery
 ~~~~~~~~~~~~~~~~
 
 Required properties :
- - compatible : "maxim,max17042"
+ - compatible : one of the following
+ * "maxim,max17042"
+ * "maxim,max17047"
+ * "maxim,max17050"
+ * "maxim,max17055"
 
 Optional properties :
  - maxim,rsns-microohm : Resistance of rsns resistor in micro Ohms