target/arm: Fix int128_make128 lo, hi order in paired_cmpxchg64_be

target/arm: Fix int128_make128 lo, hi order in paired_cmpxchg64_be

The lo,hi order is different from the comments. And in commit
1ec182c33379 ("target/arm: Convert to HAVE_CMPXCHG128"), it changes
the original code logic. So just restore the old code logic before this
commit:
do_paired_cmpxchg64_be():
    cmpv = int128_make128(env->exclusive_high, env->exclusive_val);
    newv = int128_make128(new_hi, new_lo);

This fixes a bug that would only be visible for big-endian
AArch64 guest code.

Fixes: 1ec182c33379 ("target/arm: Convert to HAVE_CMPXCHG128")
Signed-off-by: Catherine Ho <catherine.hecx@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 1548985244-24523-1-git-send-email-catherine.hecx@gmail.com
[PMM: added note that bug only affects BE guests]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>