usb: dwc2: host: disconnect hcd prior stopping it

In case controller is asked to stop while devices are connected,
disconnect all devices and clean up before stopping.

Signed-off-by: Gregory Herrero <gregory.herrero@intel.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@intel.com>
Tested-by: Robert Baldyga <r.baldyga@samsung.com>
Tested-by: Dinh Nguyen <dinguyen@opensource.altera.com>
Tested-by: John Youn <johnyoun@synopsys.com>
Acked-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>