spec: split qemu-kvm* requirement to its own %if

qemu-kvm* dependency is about to become even more complex, and as such
it is granted a special %if section.

Change-Id: I088eee894b631d9f864d6b7563877bf3ac76a9f3
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/33378
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/33406
Reviewed-by: Nir Soffer <nsoffer@redhat.com>