drivers: udc_dwc2: Arm control out endpoint in DMA mode

It was observed that device ceases to work in Buffer DMA mode after GET
DEVICE QUALIFIER request is STALLed (when USB stack is limited to
Full-Speed only operation). The issue is due to missing dout feed.

Clear pending dout feed flag after bus reset (enumeration done) and
after stalled control read transfer to allow dout to be feed when
necessary.

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>