expo: Use switch statements more for object types

expo: Use switch statements more for object types

In a lot of cases menus are the only objects which are have their own
behaviour in the cedit, e.g. to move between menus. With expo expanding
to support text, this is no-longer true.

Use a switch() statement so that we can simply insert a new 'case' for
the new object types.

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