ENGR00232755 USB: disable clock and abnormal wakeup when remove gadget driver

ENGR00232755 USB: disable clock and abnormal wakeup when remove gadget driver

- In current bsp, the usb clock mismatch when rmmod gadget class driver. The
  clock should be turn off when gadget class driver unregister.
- There is an abnormal usb wakeup interrupt happen if phy is no power without
  VBUS. If we unplug the usb cable after unregister usb gadget driver, it is
  difficult to handle the unexpected usb wakeup interrupt. SO we must call
  dr_discharge_line()  to make sure no abnormal usb wakeup interrupt happen in
  usb unregister gadget class driver.

Signed-off-by: make shi <b15407@freescale.com>