charger-manager: Use EXTCON Subsystem to detect charger cables for charging

This patch support that charger-manager use EXTCON(External Connector)
Subsystem to detect the state of charger cables for enabling or disabling
charger(regulator) and select the charger cable for charging among
a number of external cable according to policy of H/W board.

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>