usb: host: xhci: add platform driver support

This adds a fairly simple xhci-platform driver support. Currently it is
used by the dwc3 driver for supporting host mode.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
diff --git a/drivers/usb/host/Kconfig b/drivers/usb/host/Kconfig
index dd04517..b179958 100644
--- a/drivers/usb/host/Kconfig
+++ b/drivers/usb/host/Kconfig
@@ -27,6 +27,10 @@
 	  To compile this driver as a module, choose M here: the
 	  module will be called xhci-hcd.
 
+config USB_XHCI_PLATFORM
+	tristate
+	depends on USB_XHCI_HCD
+
 config USB_XHCI_HCD_DEBUGGING
 	bool "Debugging for the xHCI host controller"
 	depends on USB_XHCI_HCD