usb: xhci: move xhci.h to include usb

The xhci.h header file is currently located under drivers/usb/xhci
Move it to the include/usb folder to make it available to drivers that
are not under drivers/usb/xhci

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
diff --git a/drivers/usb/host/xhci-fsl.c b/drivers/usb/host/xhci-fsl.c
index c0b98a8..9e0c1b7 100644
--- a/drivers/usb/host/xhci-fsl.c
+++ b/drivers/usb/host/xhci-fsl.c
@@ -13,7 +13,7 @@
 #include <linux/compat.h>
 #include <linux/usb/xhci-fsl.h>
 #include <linux/usb/dwc3.h>
-#include "xhci.h"
+#include <usb/xhci.h>
 #include <fsl_errata.h>
 #include <fsl_usb.h>
 #include <dm.h>