compositor-{drm, fbdev, rpi}: Make VT switching configurable

Add a new boolean weston.ini option, "vt-switching" to enable or
disable Ctrl-Alt-Fn key combinations.

Signed-off-by: Bob Ham <bob.ham@collabora.com>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>

(Derek Foreman changed the prototype for switch_vt_binding to
have a weston_keyboard * instead of weston_seat *.  The pointer
wasn't used, so this is just a warning fix.)
diff --git a/src/launcher-util.h b/src/launcher-util.h
index a2219f6..93321ab 100644
--- a/src/launcher-util.h
+++ b/src/launcher-util.h
@@ -52,4 +52,7 @@
 void
 weston_launcher_restore(struct weston_launcher *launcher);
 
+void
+weston_setup_vt_switch_bindings(struct weston_compositor *compositor);
+
 #endif