Cpufreq: prevent negative px resident time, add spinlock to avoid race

Cpufreq: prevent negative px resident time, add spinlock to avoid race

Due to NOW() value may drift between different cpus, we add protection
to prevent negative px resident time.
Due to both cpufreq logic and xenpm may race accessing
cpufreq_statistic_data, we add spinlock to avoid race.

Signed-off-by: Liu, Jinsong <jinsong.liu@intel.com>