redhat: RHEL8 add elfutils-devel as build dependency for kernel module

redhat: RHEL8 add elfutils-devel as build dependency for kernel module

Building the kernel modules under RHEL8 produces the following error
message:
    Makefile:952: *** "Cannot generate ORC metadata for
     CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or
     elfutils-libelf-devel".  Stop.

Add elfutils-devel to the BuildRequires in the rpm spec when building
rhel >= 8

Add elfutils-devel to the BuildRequires in the rpm spec that
openafs-kmodtool produces

FIXES 134900

Reviewed-on: https://gerrit.openafs.org/13560
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 13817774518ada28f5fe68e0d00ef5dd00b67b55)

Change-Id: If4f453e6c459a2865626d4fd71bb47030e3deb58
Reviewed-on: https://gerrit.openafs.org/13563
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>