usb: dwc3: define ScaleDown macro helper

We must ensure that those bits aren't set as
they should only be used in simulation.

Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/core.h

@@ -160,6 +160,7 @@
 #define DWC3_GCTL_PRTCAP_OTG	3
 
 #define DWC3_GCTL_CORESOFTRESET	(1 << 11)
+#define DWC3_GCTL_SCALEDOWN(n)	(n << 4)
 #define DWC3_GCTL_DISSCRAMBLE	(1 << 3)
 
 /* Global USB2 PHY Configuration Register */