kbuild: add vmlinux to kernel rpm

We are building an automated system to test kernels weekly and need to
provide an rpm to our QA dept.  We would like to use the ability to create
kernel rpms already in the kernel's Makefile, but need the vmlinux file
included in the rpm for later debugging.

This patch adds a compressed vmlinux to the kernel rpm when doing a
make rpm-pkg or binrpm-pkg and upon install places the vmlinux file in /boot.

Signed-off-by: Josh Hunt <josh@scalex86.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>