charger-manager: Check fully charged state of battery periodically

This patch check periodically fully charged state of battery to protect
overcharge and overheat. If battery is fully charged, stop charging and
check droped voltage with 'fullbatt_vchkdrop_ms' period. When voltage of
battery is more droped than 'fullbatt_vchkdrop_uV' voltage,
charger-manager will restart charging for battery.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>