s390/traps: die on translation exceptions

Translation exceptions should never happen, since that implies that
either we screwed up the page tables or missed to properly flush the TLB.

In both cases we should not just simply kill user space or walk the kernel
exception tables. Instead an oops or a panic (panic_on_oops) is the better
answer.

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