usb: dwc3: gadget: Avoid starting DWC3 gadget during UDC unbind

There is a race present where the DWC3 runtime resume runs in parallel
to the UDC unbind sequence.  This will eventually lead to a possible
scenario where we are enabling the run/stop bit, without a valid
composition defined.

Thread#1 (handling UDC unbind):
usb_gadget_remove_driver()
-->usb_gadget_disconnect()
  -->dwc3_gadget_pullup(0)
--> continue UDC unbind sequence
-->Thread#2 is running in parallel here

Thread#2 (handing next cable connect)
__dwc3_set_mode()
  -->pm_runtime_get_sync()
    -->dwc3_gadget_resume()
      -->dwc->gadget_driver is NOT NULL yet
      -->dwc3_gadget_run_stop(1)
      --> _dwc3gadget_start()
...

Fix this by tracking the pullup disable routine, and avoiding resuming
of the DWC3 gadget.  Once the UDC is re-binded, that will trigger the
pullup enable routine, which would handle enabling the DWC3 gadget.

Acked-by: Felipe Balbi <[email protected]>
Signed-off-by: Wesley Cheng <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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