power: supply: core: Add one field to present the battery internal resistance

Add one field for 'struct power_supply_battery_info' to present the battery
factory internal resistance.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>