dt-bindings: power: Convert battery.txt to battery.yaml

Convert the battery.txt file to yaml and fix up the examples.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
[Fixed the regex for ocv-capacity-table and the DT example for it]
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>