expo: Test some cedit actions

Refactor the action-processing code into a new cedit_do_action()
function so we can call it from a test. Check moving to a new field and
opening the menu, to ensure that rendering is correct.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/cedit.h b/include/cedit.h
index 856509f..a9305ce 100644
--- a/include/cedit.h
+++ b/include/cedit.h
@@ -13,6 +13,7 @@
 
 struct abuf;
 struct expo;
+struct expo_action;
 struct scene;
 struct udevice;
 struct video_priv;
@@ -63,6 +64,18 @@
 		  struct scene **scnp);
 
 /**
+ * cedit_do_action() - Process an action on a cedit
+ *
+ * @exp: Expo to use
+ * @scn: Current scene
+ * @vid_priv: Private data for the video device
+ * @act: Action to process
+ * Return: 0 on success, -EAGAIN if there was no action taken
+ */
+int cedit_do_action(struct expo *exp, struct scene *scn,
+		    struct video_priv *vid_priv, struct expo_action *act);
+
+/**
  * cedit_write_settings() - Write settings in FDT format
  *
  * Sets up an FDT with the settings