The BINARY files given in the config files are expected to be relative
to the place kwbimage is called from. This is bad since it breaks where
kwbimage is called from the build directory and not the source
directory.
It makes more sense to make the paths in the config files relative
to the config files which works with out of tree builds and is also
more what a user normally expects.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>