expo: Draw the current opened menu on top

expo: Draw the current opened menu on top

When a menu is opened, it must be displayed over all other objects in
the scene, so that all its items are visible.

Handle this by drawing the menu object a second time, after all other
objects have been drawn. Draw all of the objects which are dependent
on the menu object.

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