s390/extable: sort amode31 extable early

The early program check handler is active before the amode31 extable
is sorted. Therefore in case a program check happens early within the
amode31 code the extable entry might not be found.

Fix this by sorting the amode31 extable early.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>