power: supply: add sbs-charger driver

This adds support for sbs-charger compilant chips as defined here:
http://sbs-forum.org/specs/sbc110.pdf



This was tested on a arm board connected to an LTC4100 battery charger
chip.

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