target/s390x: check alignment in CDSG in the !CONFIG_ATOMIC128 case

The CDSG instruction requires a 16-byte alignement, as expressed in
the MO_ALIGN_16 passed to helper_atomic_cmpxchgo_be_mmu. In the non
parallel case, use check_alignment to enforce this.
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
Message-Id: <20170604202034.16615-4-aurelien@aurel32.net>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

target/s390x/mem_helper.c

@@ -1262,6 +1262,8 @@ void HELPER(cdsg)(CPUS390XState *env, uint64_t addr,
     } else {
         uint64_t oldh, oldl;
 
+        check_alignment(env, addr, 16, ra);
+
         oldh = cpu_ldq_data_ra(env, addr + 0, ra);
         oldl = cpu_ldq_data_ra(env, addr + 8, ra);