s390: wire up sys_renameat2

Actually this also enable sys_setattr and sys_getattr, since I forgot to
increase NR_syscalls when adding those syscalls.

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