s390/atomic: Provide arch_atomic_try_cmpxchg()

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

Provide an arch_atomic try_cmpxchg() implementation so that all
existing atomic_try_cmpxchg() usages generate 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>