[S390] zfcpdump: Do not initialize zfcpdump in kdump mode

When the kernel is started in kdump mode, zfcpdump should not be
initialized because both dump methods can't be used at the same time.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>