usb: dwc2: gadget: Prevent wrong extcon notification

usb: dwc2: gadget: Prevent wrong extcon notification

In sometimes, USB disconnection triggers enumeration-done interrupt
even though it is false state. Actually, this interrupt is ignored by
dwc2 irq handler, but extcon notfication can be mis-delivered to
user-space. Thus, this patch make worker determined the current state
by itself, and it also prevent some cases which have chance for wrong
notification such as repeatedly connect/disconnecting usb cable.

Change-Id: Iff88cf2c030b627f3d2da23930b10e9f3a84c8e1
Signed-off-by: Dongwoo Lee <dwoo08.lee@samsung.com>