usb: host: xhci-plat: add wakeup entry at sysfs

usb: host: xhci-plat: add wakeup entry at sysfs

With this change, there will be a wakeup entry at /sys/../power/wakeup,
and the user could use this entry to choose whether enable xhci wakeup
features (wake up system from suspend) or not.

Tested-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20200918131752.16488-6-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>