ENGR00179679 Fix usb gadget suspend issue connected to usb charger

ENGR00179679 Fix usb gadget suspend issue connected to usb charger

- the root cause of this issue is during resume process, USB clock
 is not turned on for this USB charger case so that the second
 suspend is processed without USB clock, it cause system hang
- in udc resume process, at this situation, we should exit low
 power mode to enable the b session valid intrrupt to close the
 usb clock when detach from usb charger

Signed-off-by: Tony LIU <junjie.liu@freescale.com>