This will allow to use the following construct in source files:

config FOO
    string
    default "foo"

source "$FOO/Kconfig"
Signed-off-by: NArnaud Lacombe <lacombar@gmail.com>
Reviewed-by: NSam Ravnborg <sam@ravnborg.org>
Reviewed-by: NMichal Marek <mmarek@suse.cz>