power: supply: ab8500: Standardize alert mode charging

The AB8500 code is using a special current and voltage setting
when the battery is in "alert mode", i.e. when it is starting
to go outside normal operating conditions so it is too
cold or too hot. This makes sense as a way for the charging
algorithm to deal with hostile environments.

Add the needed members to the struct power_supply_battery_info,
and switch the AB8500 charging code over to using this.

Reviewed-by: Matti Vaittineen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>