tcg: Split out tcg_gen_nonatomic_cmpxchg_i{32,64}

tcg: Split out tcg_gen_nonatomic_cmpxchg_i{32,64}

Normally this is automatically handled by the CF_PARALLEL checks
with in tcg_gen_atomic_cmpxchg_i{32,64}, but x86 has a special
case of !PREFIX_LOCK where it always wants the non-atomic version.

Split these out so that x86 does not have to roll its own.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>