dt-bindings: power: supply: sbs-charger bindings

Adds device tree documentation for SBS charger compilant devices as defined
here: http://sbs-forum.org/specs/sbc110.pdf



Signed-off-by: Nicolas Saenz Julienne <nicolas.saenz@prodys.net>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>