usb: chipidea: add usb as system wakeup source

The USB signal can be system wakeup source, this patch add the
support, for how to enable it, see Documentation/usb/chipidea.txt.
Since USB wakeup enable logic is vendor/platform specific, the
glue layer needs to implement it to support this feature.

Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>