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/Makefile b/drivers/usb/host/Makefile
index 7ca290f..0982bcc 100644
--- a/drivers/usb/host/Makefile
+++ b/drivers/usb/host/Makefile
@@ -15,6 +15,10 @@
 xhci-hcd-y += xhci-ring.o xhci-hub.o xhci-dbg.o
 xhci-hcd-$(CONFIG_PCI)	+= xhci-pci.o
 
+ifneq ($(CONFIG_USB_XHCI_PLATFORM), )
+	xhci-hcd-y		+= xhci-plat.o
+endif
+
 obj-$(CONFIG_USB_WHCI_HCD)	+= whci/
 
 obj-$(CONFIG_PCI)		+= pci-quirks.o