expo: Convert to using a string ID for the scene title

This is easier to deal with if it uses the existing string handling,
since we will be able to use translations, etc. in the future.

Update it to use an ID instead of a string.

Signed-off-by: Simon Glass <sjg@chromium.org>

boot/scene.c

@@ -65,16 +65,12 @@ void scene_destroy(struct scene *scn)
 		scene_obj_destroy(obj);
 
 	free(scn->name);
-	free(scn->title);
 	free(scn);
 }
 
-int scene_title_set(struct scene *scn, const char *title)
+int scene_title_set(struct scene *scn, uint id)
 {
-	free(scn->title);
-	scn->title = strdup(title);
-	if (!scn->title)
-		return log_msg_ret("tit", -ENOMEM);
+	scn->title_id = id;
 
 	return 0;
 }