Introduce a menu framework that allow us to create list menu to simplify
barebox and make it more user-frendly

This kind of menu is very usefull when you do not have a keyboard or a
serial console attached to your board to allow you to interract with
barebox

For the develloper part,
The framework introduce two API

1) C
that allow you to create menu, submenu, entry and complex menu action

2) Command
that allow you as the C API to create menu, submenu, entry and complex
menu action but this time the actions will be store in a function and
then be evaluated and excecuted at runtime.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>