s390/crash dump: add missing SMP dependency

Fix this:
arch/s390/kernel/crash_dump.c:296:14:
  error: 'zfcpdump_save_areas' undeclared (first use in this function)

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