usb: dwc2: gadget: Correct dwc2_hsotg_ep_stop_xfr() function

Correct dwc2_hsotg_ep_stop_xfr() function to follow dwc2 programming
guide for setting NAK on specific endpoint, disabling it and flushing
corresponding FIFO.

Current code does not take into account whether core acts in shared or
dedicated FIFO mode, current endpoint is periodic or not. It does not
clear EPDISBLD interrupt after programming of DXEPCTL_EPDIS, does not
flush shared TX FIFO and tries to clear global out NAK in wrong manner
instead of setting DCTL_CGOUTNAK.

Signed-off-by: Vahram Aharonyan <vahrama@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>