[S390] Print kernel version in dump_stack() and show_regs().

Also print PREEMPT and/or SMP if the kernel was configured that way.
Makes s390 look a bit more like other architectures.

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