ab8500-charger: AB8500 charger driver

This driver is responsible for detecting the ac/usb plugin and also includes
function to enable ac/usb charging and re-kick the watchdog.
It registers with the power supply class and provides information to the user
space. The information include status of ac/usb charger device.
This information in turn will be used by the abx500 charging algorithm driver
to enable/disable and monitor charging.

Signed-off-by: Arun Murthy <arun.murthy@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>