usb: dwc3: debug: move dwc3_ep0_state_string() to debug.h

We will be using dwc3_ep0_state_string() from within
our tracepoints, so we need to move that helper to
debug.h in order for it to be accessible.

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/debug.h

@@ -124,6 +124,22 @@ dwc3_gadget_link_string(enum dwc3_link_state link_state)
 	}
 }
 
+static inline const char *dwc3_ep0_state_string(enum dwc3_ep0_state state)
+{
+	switch (state) {
+	case EP0_UNCONNECTED:
+		return "Unconnected";
+	case EP0_SETUP_PHASE:
+		return "Setup Phase";
+	case EP0_DATA_PHASE:
+		return "Data Phase";
+	case EP0_STATUS_PHASE:
+		return "Status Phase";
+	default:
+		return "UNKNOWN";
+	}
+}
+
 /**
  * dwc3_gadget_event_string - returns event name
  * @event: the event code