s390/traps: preinitialize program check table

Preinitialize the program check table, so we can put it into the
read-only data section.
Also use only four byte entries for the table, since each program
check handler resides within the first 2GB. Therefore this reduces
the size of the table by 50% on 64 bit builds.

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