zephyr: USB: DW driver does not work properly with mass storage class

DW USB device driver does not work properly with mass storage class (MSC).

Tested with sample/subsys/usb/mass on Arduino 101 connected to Linux host:

• does not work on UHCI. Arduino 101 flashed with the sample can be enumerated by the host, after detecting the mass storage device, the host resets the device several times because the device stops respond to requests. Works sometimes (mount, read and write to partition) on UHCI with path introduced in #5496.
• does not work on XHCI. Behavior is similar to above, in addition, the partition will not be detected. There is also a note in sample/subsys/usb/mass/README.txt about issues with Arduino 101.

I have also tested sample/subsys/usb/mass on FRDM-K64F with #542 and I have not observed any problems with Linux and Windows 7 host.

Similar behavior was observed under Windows OS, see #5496