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>

drivers/usb/musb/da8xx.c

@@ -33,6 +33,7 @@
 #include <linux/io.h>
 #include <linux/platform_device.h>
 #include <linux/dma-mapping.h>
+#include <linux/usb/nop-usb-xceiv.h>
 
 #include <mach/da8xx.h>
 #include <mach/usb.h>