cpufreq: move policy kobj to update_policy_cpu()

We are calling kobject_move() from two separate places currently and both these
places share another routine update_policy_cpu() which is handling everything
around updating policy->cpu. Moving ownership of policy->kobj also lies under
the role of update_policy_cpu() routine and must be handled from there.

So, Lets move kobject_move() to update_policy_cpu() and get rid of
cpufreq_nominate_new_policy_cpu() as it doesn't have anything significant left.

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