target/sparc: check CF_PARALLEL instead of parallel_cpus

Thereby decoupling the resulting translated code from the current state
of the system.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
