Convert busybox to the device declaration method

Busybox used to declare and create files even if the package was not
enabled through the device table. Remove the entries for busybox in the
device table and move them to the package declaration.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>