usb: dwc3: gadget: Allow runtime suspend if UDC unbinded

The DWC3 runtime suspend routine checks for the USB connected parameter to
determine if the controller can enter into a low power state.  The
connected state is only set to false after receiving a disconnect event.
However, in the case of a device initiated disconnect (i.e. UDC unbind),
the controller is halted and a disconnect event is never generated.  Set
the connected flag to false if issuing a device initiated disconnect to
allow the controller to be suspended.

Signed-off-by: Wesley Cheng <wcheng@codeaurora.org>
Link: https://lore.kernel.org/r/1609283136-22140-2-git-send-email-wcheng@codeaurora.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>