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/musb_dsps.c b/drivers/usb/musb/musb_dsps.c
index 217808d..4e899bb 100644
--- a/drivers/usb/musb/musb_dsps.c
+++ b/drivers/usb/musb/musb_dsps.c
@@ -36,6 +36,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/pm_runtime.h>
 #include <linux/module.h>
+#include <linux/usb/nop-usb-xceiv.h>
 
 #include <linux/of.h>
 #include <linux/of_device.h>