usb: xceiv: create nop-usb-xceiv.h and avoid pollution on otg.h

nop-usb-xceiv was polluting otg.h with its own
function prototypes. Move those prototypes to
a nop-usb-xceiv.h header.

Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/musb/tusb6010.c b/drivers/usb/musb/tusb6010.c
index 1a1bd9c..00f21df 100644
--- a/drivers/usb/musb/tusb6010.c
+++ b/drivers/usb/musb/tusb6010.c
@@ -24,6 +24,7 @@
 #include <linux/irq.h>
 #include <linux/platform_device.h>
 #include <linux/dma-mapping.h>
+#include <linux/usb/nop-usb-xceiv.h>
 
 #include "musb_core.h"