usb: xhci: define port register names and use them instead of magic numbers

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 66b048a..0132571 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -132,6 +132,11 @@
 /* Number of registers per port */
 #define	NUM_PORT_REGS	4
 
+#define PORTSC		0
+#define PORTPMSC	1
+#define PORTLI		2
+#define PORTHLPMC	3
+
 /**
  * struct xhci_op_regs - xHCI Host Controller Operational Registers.
  * @command:		USBCMD - xHC command register