-------------- barebox consoles ------------------

barebox supports multiple consoles which may be simultaneously active.
Depending on the configuration none, the first or all consoles are
activated on startup, see CONSOLE_ACTIVATE_FIRST and CONSOLE_ACTIVATE_ALL
options.

During runtime the behaviour of the consoles can be controlled with the
'active' parameter each console has. The console system recognizes three
characters: 'i' for stdin, 'o' for stdout and 'e' for stderr. These options
may be concatenated together as needed, so setting an 'active' parameter
of a console to 'io' would enable it for stdout and stdin while leaving
stderr disabled.