0e2b490 introduced rework of usb driver which was broken. It was reverted
in f2da975 to restore hwstub functionality on ATJ.
This commit reenables usb rework AND fixes remining issues.
The problem was with 0 length OUT thransfers. Additionally
a few cleanups were made.
Change-Id: I529ea9ad6540509e9287ca7e1cd2b44369b03cbb