s390/kernel: expand exception table logic to allow new handling options

This is a s390 port of commit 548acf19 ("x86/mm: Expand the
exception table logic to allow new handling options"), which is needed
for implementing BPF_PROBE_MEM on s390.

The new handler field is made 64-bit in order to allow pointing from
dynamically allocated entries to handlers in kernel text. Unlike on x86,
NULL is used instead of ex_handler_default. This is because exception
tables are used by boot/text_dma.S, and it would be a pain to preserve
ex_handler_default.

The new infrastructure is ignored in early_pgm_check_handler, since
there is no pt_regs.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>