This will be of small comfort to sparc64, because both
sun4u and sun4v board models force max_cpus = 1.
But it does enable actual smp for sparc32 sun4m.

Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Acked-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>