usb: dwc_otg: Set extcon state for usb cable as always true

usb: dwc_otg: Set extcon state for usb cable as always true

To inform to userspace as enable usb features always, set extcon
state for usb cable as connected permanently. To enable this, add
g-extcon-always-on property on dt.

Note: ported from https://git.tizen.org/cgit/profile/common/platform/kernel/linux-artik7/commit/?h=tizen&id=f7e1e93b230f61d66d6a3bc58d09c53dcd305e21

Change-Id: I16fb629ccec54f0ae46e697b56750c3021f01ccb
Signed-off-by: Dongwoo Lee <dwoo08.lee@samsung.com>
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>