ENGR00212992 usb: fix potential bug with fast plug in/out with usb charger

ENGR00212992 usb: fix potential bug with fast plug in/out with usb charger

- Move imx_usb_vbus_disconnect to work queue, and wait or cancel
charger detect worker when vbus is disconnected if charger detect
worker still hasn't finished.
- Move pull down dp from imx_usb_vbus_disconnect to udc vbus
disconnect interrupt handler, the reason is udc->gadget.speed should
to be updated at that ISR.
- Select POWER_SUPPLY if USB_GADGET_ARC is configured to fix the build
error for manufacture tools firmware's build.

Signed-off-by: Peter Chen <peter.chen@freescale.com>