[S390] mutex: enable spinning mutex on s390

This enables the spinning mutex feature on s390 by removing
HAVE_DEFAULT_NO_SPIN_MUTEXES from arch/s390/Kconfig.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>