rpm-pkg: add generation of kernel-devel

Change the spec file to generate a kernel-devel module
allowing for compilation of external kernel modules.

This patch requires a new minimum RPM level of 4.0.3.

Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>