s390/jump_label: replace stop_machine with smp_call_function

The use of stop_machine to replace the mask bits of the jump label branch
is a very heavy-weight operation. This is in fact not necessary, the
mask of the branch can simply be updated, followed by a signal processor
to all the other CPUs to force them to pick up the modified instruction.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
[heiko.carstens@de.ibm.com]: Change jump_label_make_nop() so we get
                             brcl 0,offset instead of brcl 0,0. This
                             makes sure that only the mask part of the
                             instruction gets changed when updated.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>