cpufreq: move some initialization stuff to cpufreq_policy_alloc()

We need to initialize completion and work only on policy allocation and not
really on the policy restore side and so we better move this piece of code to
cpufreq_policy_alloc().

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>