[S390] topology: fix topology on z10 machines

Make sure that all cpus in a book on a z10 appear as book siblings
and not as core siblings. This fixes some performance regressions that
appeared after the book scheduling domain got introduced.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>