fixdep: fix extraneous dependencies

The introduction of include/linux/kconfig.h created 3 extraneous
dependencies:
include/config/.h
include/config/h.h
include/config/foo.h

Fix this by excluding kconfig.h from fixdep calculations.

Signed-off-by: Peter Foley <pefoley2@verizon.net>
Signed-off-by: Michal Marek <mmarek@suse.cz>