cpufreq: allocate CPU masks dynamically

cpufreq: allocate CPU masks dynamically

struct cpufreq_policy, including a cpumask_t member, gets copied in
cpufreq_limit_change(), cpufreq_add_cpu(), set_cpufreq_gov(), and
set_cpufreq_para(). Make the member a cpumask_var_t, thus reducing the
amount of data needing copying (particularly with large NR_CPUS).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>