power_supply: Add bq2415x charger driver

The bq2415x charger driver is needed for example on Nokia N900 for
charging battery. Driver is part of open source project to replace
proprietary battery management.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>