usb: mtu3: handle delayed status of the control transfer

Add the delayed status handling. This is used by mass storage etc to
gain some extra time to setup its internal status before it can proceed
further requests, and once the gadget is ready, it will enqueue an
empty packet which is used for synchronization.
The issue may happen on some FGPA platform with very low cpu frequency.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>