It has been noticed that the dwc2 udc state reporting doesn't
seem to work (at least on HiKey boards). Where after the initial
setup, the sysfs /sys/class/udc/f72c0000.usb/state file would
report "configured" no matter the state of the OTG port.

This patch adds a call so that we report to the UDC layer when
the gadget device is disconnected.

This patch does depend on the previous patch ("usb: dwc2:
Improve gadget state disconnection handling") in this patch set
in order to properly work.

Cc: Wei Xu <xuwei5@hisilicon.com>
Cc: Guodong Xu <guodong.xu@linaro.org>
Cc: Amit Pundir <amit.pundir@linaro.org>
Cc: YongQin Liu <yongqin.liu@linaro.org>
Cc: John Youn <johnyoun@synopsys.com>
Cc: Minas Harutyunyan <Minas.Harutyunyan@synopsys.com>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Chen Yu <chenyu56@huawei.com>
Cc: Felipe Balbi <felipe.balbi@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Tested-by: Minas Harutyunyan <hminas@synopsys.com>
Reported-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>