Makefile.inc: Add dependency on util/kconfig/conf for config.h

This dependency wasn't called out before, and when building with enough
threads, the build would fail due to a collision trying to build
build/util/kconfig/conf.

Fixes this failure:
make[1]: execvp: build/util/kconfig/conf: Permission denied
/home/martin/git/coreboot/util/kconfig/Makefile:40: recipe for target
'oldconfig' failed
make[1]: *** [oldconfig] Error 127
Makefile:167: recipe for target 'build/config.h' failed

Change-Id: Ib78d36bab0ba469796d89877bbe6a61e05196e87
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/13859
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
1 file changed