This should ideally be done once after all scene changes have been made.
Require an explicit call when everything is ready.
Always arrange after a key it sent, just for convenience.
Signed-off-by: Simon Glass <sjg@chromium.org>
This is easier to deal with if it uses the existing string handling,
since we will be able to use translations, etc. in the future.
Update it to use an ID instead of a string.
Signed-off-by: Simon Glass <sjg@chromium.org>
A scene is a single screen within an expo. It is possible to move between
scenes but only one can be displayed at once.
Add a basic implementation.
Signed-off-by: Simon Glass <sjg@chromium.org>