usb: dwc3: ep0: don't change to configured state too early

before changing to configured state, we need
to wait until gadget driver has had a chance
to process the request.

In case of USB_GADGET_DELAYED_STATUS, that means
we need to defer usb_gadget_set_state() until
the upcoming usb_ep_queue().

Reported-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Felipe Balbi <balbi@ti.com>