makefile: allow to disable all default-yes config variables with CONFIG_NOTHING=yes

All credit for this should be given to Patrick Georgi (see r1869).

Corresponding to flashrom svn r1944.

Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
1 file changed