usb: xhci: Add helper function xhci_disable_slot().

Refactoring slot disable related code into a helper
function xhci_disable_slot() which can be used when
enabling test mode.

Signed-off-by: Guoqing Zhang <guoqing.zhang@intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index da3eb69..d3485f8 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -2018,6 +2018,8 @@ void xhci_shutdown(struct usb_hcd *hcd);
 int xhci_gen_setup(struct usb_hcd *hcd, xhci_get_quirks_t get_quirks);
 void xhci_init_driver(struct hc_driver *drv,
 		      const struct xhci_driver_overrides *over);
+int xhci_disable_slot(struct xhci_hcd *xhci,
+			struct xhci_command *command, u32 slot_id);
 
 #ifdef	CONFIG_PM
 int xhci_suspend(struct xhci_hcd *xhci, bool do_wakeup);