dix: Move DeviceFocusEvent from Xi into enterleave.c

This is only called from the enterleave implementation, so move it and its
helper functions to there. No functional changes.

Fixes build error introduced in 31174565ec if
building with '-Werror=implicit-function-declaration'

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Jeremy Huddleston <jeremyhu@apple.com>

dix/enterleave.h

@@ -52,6 +52,11 @@ extern void DeviceEnterLeaveEvent(DeviceIntPtr mouse,
                                   int type,
                                   int mode,
                                   int detail, WindowPtr pWin, Window child);
+extern void DeviceFocusEvent(DeviceIntPtr dev,
+                             int type,
+                             int mode,
+                             int detail ,
+                             WindowPtr pWin);
 
 extern void EnterWindow(DeviceIntPtr dev, WindowPtr win, int mode);