s390/cmpxchg: Provide arch_try_cmpxchg()

Since gcc 14 flag output operands are supported also for s390.

Provide an arch_try_cmpxchg() implementation so that all existing
try_cmpxchg() variants provide slightly better code, if compiled
with gcc 14 or newer.

Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>