extcon: Add missing header file to extcon.h

This patch add missing header file(sysfs.h/device.h) to extcon.h
because 'struct extcon_dev' define attribute field(attr_g_muex/
attrs_muex/d_attrs_mues) and device_type field(extcon_dev_type).

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