s390/uprobes: implement arch_uretprobe_is_alive()

s390/uprobes: implement arch_uretprobe_is_alive()

Implement s390 specific arch_uretprobe_is_alive() to avoid SIGSEGVs
observed with uretprobes in combination with setjmp/longjmp.

See commit 2dea1d9c38e4 ("powerpc/uprobes: Implement
arch_uretprobe_is_alive()") for more details.

With this implemented all test cases referenced in the above commit
pass.

Reported-by: Ziqian SUN <[email protected]>
Cc: <[email protected]> # v4.3+
Signed-off-by: Heiko Carstens <[email protected]>
Signed-off-by: Martin Schwidefsky <[email protected]>