ENGR00234722 USB: fix Kernel dump issue after USB driver loadable

ENGR00234722 USB: fix Kernel dump issue after USB driver loadable

- It is better to disable otgsc and wake up interrupt to avoid an
  abnormal interrupt happen during USB driver being removed.
- If the USB host is already at low power mode, only need turn on
  the clock, no need turn off the clock.
- Need discharge dp and dm during USB driver being removed ,in order
  to avoid a wakeup interrupt happen. And if the USB otg is in host
  mode, we should clear discharge dp and dm in fsl_otg_set_host()
  during system boot up.

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