power: supply: sc27xx: Add fuel gauge low voltage alarm

Add low voltage alarm support to make sure the battery capacity
more accurate in lower voltage stage.

Signed-off-by: Yuanjiang Yu <yuanjiang.yu@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>