s390/compat: change default for CONFIG_COMPAT to "n"

31 bit support has been removed from the kernel more than eight years
ago. The last 31 bit distribution is many years older. There shouldn't be
any 31 bit code around anymore.

Therefore avoid providing an unused and only partially tested user space
interface and change the default for CONFIG_COMPAT from "yes" to "no".

Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>