usb: dwc2: gadget: Add EP disabled interrupt handler

Reimplemented EP disabled interrupt handler and moved to
corresponding function.

This interrupt indicates that the endpoint has been disabled per
the application's request.

For IN endpoints flushes txfifo, in case of BULK clears DCTL_CGNPINNAK,
in case of ISOC completes current request.

For ISOC-OUT endpoints completes expired requests. If there is
remaining request starts it. This is the part of ISOC-OUT transfer
drop flow. When ISOC-OUT transfer expired we must disable ep to drop
ongoing transfer.

Tested-by: John Keeping <john@metanate.com>
Reviewed-by: Vahram Aharonyan <vahrama@synopsys.com>
Signed-off-by: Vardan Mikayelyan <mvardan@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>