PM / devfreq: passive: Keep cpufreq_policy for possible cpus

The passive governor requires the cpu data to get the next target frequency
of devfreq device if depending on cpu. In order to reduce the unnecessary
memory data, keep cpufreq_policy data for possible cpus instead of NR_CPU.

Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Tested-by: Johnson Wang <johnson.wang@mediatek.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>