usb: dwc3: core: support DRD mode switch with extcon notifier

usb: dwc3: core: support DRD mode switch with extcon notifier

This patch register extcon notification for DRD mode.
If extcon cable state is EXTCON_USB, means that an USB
peripheral cable connected, and we need to set DWC3 work
in device mode. If extcon cable state is EXTCON_USB_HOST,
means that an USB host cable connected, and we need to
set DWC3 work in host mode.

And we need to register different notifier block for
EXTCON_USB notifier and EXTCON_USB_HOST notifier，because
if multiple notifiers registered with the same notifier
block, it will cause kernel crash on notification events.

Change-Id: Ia09e5088f738496b87d06b0f4062c144fa781e4e
Signed-off-by: Wu Liang feng <wulf@rock-chips.com>