dt-bindings: power: supply: Cleanup charger-manager bindings

The bindings for charger-manager were very unclear and didn't
specify allowable values in many cases.  Clean these up to show
what each value does and make sure all properties are documented
here rather than using wildcards.

Signed-off-by: Jonathan Bakker <xc-racer2@live.ca>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>