usb: gadget: udc: net2280: Merge abort_dma for 228x and 338x

We can use the same function for both families of chips and also remove
the ep_stop_dma() function.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>