makefile: not need to regenerate kernel.release file when make kernelrelease

Brice reported that 'kernelrelease' has a dependence on include/config/kernel.release,
causes this file to be regenerated every time when invoke it. It doesn't have to.

Reported-by: Brice Goglin <Brice.Goglin@inria.fr>
Tested-by: Brice Goglin <Brice.Goglin@inria.fr>
Signed-off-by: WANG Cong <amwang@redhat.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>