usb: chipidea: otg: gadget module load and unload support

commit 85da852d upstream.

This patch is to support load and unload gadget driver in full OTG mode.

Signed-off-by: Li Jun <jun.li@freescale.com>
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Tested-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>