Within tests it is useful to be able to control rendering of the expo.
Drop the automatic call to expo_render() within expo_poll() and adjust
its callers to handle this instead.

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

Expo normally uses a pointer to show the current item. Add support for
highlighting as well, since this makes it easier for the user to see the
current item.

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

It is useful to be able to edit text, e.g. to allow the user to edit the
environment or the command-line arguments for the OS.

Add the beginnings of an implementation. Future work is needed to finish
this: keypress handling and scrolling. For now it just displays the
text.

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

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>

In preparation for adding more text types, refactor the common fields
into a new structure. This will allow common code to be used.

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

At present when the user moves to a new menu item, the menu code
handles this immediately. This means it is not possible to use an expo
action to effect the same change.

Update this so that EXPOACT_POINT_ITEM is handled in cedit_do_action().

Expand the test to cover this.

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

At present this function locates it own video device. Pass it in to
provide more flexibility.

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

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>

Move the boolean flags into struct expo so that the state can be
maintained over function calls.

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

Both bootflow_menu and cedit use similar logic to poll an expo. Move
this into the expo library so the code can be shared.

Update bootflow_menu_run() to return -EPIPE when the user quits without
choosing anything, since -EAGAIN is ambiguous and elsewhere means that
there is no input yet.

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