dt-bindings: olpc_battery: Add XO-1.5 battery

The XO-1 and XO-1.5 batteries apparently differ in an ability to report
ambient temperature.
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

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

@@ -2,4 +2,4 @@ OLPC battery
 ~~~~~~~~~~~~
 
 Required properties:
-  - compatible : "olpc,xo1-battery"
+  - compatible : "olpc,xo1-battery" or "olpc,xo1.5-battery"