expo: Create a struct for generic text attributes

In preparation for adding more text types, refactor the common fields
into a new structure. This will allow common code to be used.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/expo.h b/include/expo.h
index 990cb30..32d69f2 100644
--- a/include/expo.h
+++ b/include/expo.h
@@ -291,23 +291,32 @@
 };
 
 /**
- * struct scene_obj_txt - information about a text object in a scene
- *
- * This is a single-line text object
+ * struct scene_txt_generic - Generic information common to text objects
  *
- * @obj: Basic object information
  * @str_id: ID of the text string to display
  * @font_name: Name of font (allocated by caller)
  * @font_size: Nominal size of font in pixels
  */
-struct scene_obj_txt {
-	struct scene_obj obj;
+struct scene_txt_generic {
 	uint str_id;
 	const char *font_name;
 	uint font_size;
 };
 
 /**
+ * struct scene_obj_txt - information about a text object in a scene
+ *
+ * This is a single-line text object
+ *
+ * @obj: Basic object information
+ * @gen: Generic information common to all objects which show text
+ */
+struct scene_obj_txt {
+	struct scene_obj obj;
+	struct scene_txt_generic gen;
+};
+
+/**
  * struct scene_obj_menu - information about a menu object in a scene
  *
  * A menu has a number of items which can be selected by the user