bq27x00_battery: Add support for BQ27425 chip

This patch adds support for BQ27425 (TI) chip. This chip is same as
BQ27500 with few registers removed and register address map changed.
The data sheet for this chip is publicly available at
 http://www.ti.com/product/bq27425-g1

Signed-off-by: Saranya Gopal <saranya.gopal@intel.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>