s390/jump label,nss: let shared kernel support depend on !JUMP_LABEL

We can have either shared kernel or jump label support, but not both.
If a kernel gets IPL'ed from an NSS it's not possible to patch the
text segment, since it's read-only.
Therefore any static branches cannot be updated. So we need to make
sure that shared kernel support is disabled if jump label support
is enabled.

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