expo: Implement a box

It is useful to be able to draw a box around elements in the menu. Add
support for an unfilled box with a selectable thickness.

Note that there is no support for selecting the colour for any expo
objects yet.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/cedit.c b/boot/cedit.c
index 0f7a865..9153fe7 100644
--- a/boot/cedit.c
+++ b/boot/cedit.c
@@ -81,6 +81,7 @@
 		case SCENEOBJT_NONE:
 		case SCENEOBJT_IMAGE:
 		case SCENEOBJT_TEXT:
+		case SCENEOBJT_BOX:
 			break;
 		case SCENEOBJT_MENU:
 			scene_obj_set_pos(scn, obj->id, 50, y);
@@ -381,6 +382,7 @@
 	case SCENEOBJT_NONE:
 	case SCENEOBJT_IMAGE:
 	case SCENEOBJT_TEXT:
+	case SCENEOBJT_BOX:
 		break;
 	case SCENEOBJT_TEXTLINE: {
 		const struct scene_obj_textline *tline;
@@ -480,6 +482,7 @@
 	case SCENEOBJT_NONE:
 	case SCENEOBJT_IMAGE:
 	case SCENEOBJT_TEXT:
+	case SCENEOBJT_BOX:
 		break;
 	case SCENEOBJT_TEXTLINE: {
 		const struct scene_obj_textline *tline;
@@ -551,6 +554,7 @@
 	case SCENEOBJT_NONE:
 	case SCENEOBJT_IMAGE:
 	case SCENEOBJT_TEXT:
+	case SCENEOBJT_BOX:
 		break;
 	case SCENEOBJT_MENU:
 		menu = (struct scene_obj_menu *)obj;
@@ -634,6 +638,7 @@
 	case SCENEOBJT_NONE:
 	case SCENEOBJT_IMAGE:
 	case SCENEOBJT_TEXT:
+	case SCENEOBJT_BOX:
 		break;
 	case SCENEOBJT_MENU:
 		menu = (struct scene_obj_menu *)obj;