power: supply: sc27xx: Optimize the battery capacity calibration

This patch factors out the capacity calibration into one single function
to calibrate the battery capacity, and adding more abnormal cases to
calibrate the capacity when the OCV value is not matchable with current
capacity.

Moreover we also allow to calibrate the capacity when charger magager
tries to get current capacity to make sure we give a correct capacity
for userspace.

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>