USB: Add empty functions in otg.h

Add empty functions for usb_nop_xceiv_register()
and usb_nop_xceiv_unregister() in otg.h so that
these functions can be called even when
CONFIG_NOP_USB_XCEIV is not enabled.

It allows to remove ifdef's from board file.

Signed-off-by: Maulik Mankad <x0082077@ti.com>
Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Ajay Kumar Gupta <ajay.gupta@ti.com>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Felipe Balbi <felipe.balbi@nokia.com>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>

include/linux/usb/otg.h

@@ -110,9 +110,19 @@ struct otg_transceiver {
 /* for board-specific init logic */
 extern int otg_set_transceiver(struct otg_transceiver *);
 
+#if defined(CONFIG_NOP_USB_XCEIV) || defined(CONFIG_NOP_USB_XCEIV_MODULE)
 /* sometimes transceivers are accessed only through e.g. ULPI */
 extern void usb_nop_xceiv_register(void);
 extern void usb_nop_xceiv_unregister(void);
+#else
+static inline void usb_nop_xceiv_register(void)
+{
+}
+
+static inline void usb_nop_xceiv_unregister(void)
+{
+}
+#endif
 
 /* helpers for direct access thru low-level io interface */
 static inline int otg_io_read(struct otg_transceiver *otg, u32 reg)