builds.
When building multiple u-boots they get compiled externally into a
directory named after machine defconfigs.
Once there is a directory with the same name as a defconfig it is not
possible to run the defconfig make target.
This change should be only temporary until it gets upstream.
Fixes https://jira.digi.com/browse/DEL-2644
Signed-off-by: Alex Gonzalez <alex.gonzalez@digi.com>