extcon: max8997: Use workqueue to check cable state after completing boot of platform

This patch use delayed workqueue to check cable state after a certain
time. If extcon-max8997 driver check cable state during booting of
platform, this couldn't send the correct notification of cable state
to extcon consumer. Alwasys, this driver should check cable state
after the completion of platform initialization

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>