cpufreq: schedutil: Fix sugov_start versus sugov_update_shared race

With a shared policy in place, when one of the CPUs in the policy is
hotplugged out and then brought back online, sugov_stop and
sugov_start are called in order.

sugov_stop removes utilization hooks for each CPU in the policy and
does nothing else in the for_each_cpu loop. sugov_start on the other
hand iterates through the CPUs in the policy and re-initializes the
per-cpu structure _and_ adds the utilization hook. This implies that
the scheduler is allowed to invoke a CPU's utilization update hook
when the rest of the per-cpu structures have yet to be re-inited.

Apart from some strange values in tracepoints this doesn't cause a
problem, but if we do end up accessing a pointer from the per-cpu
sugov_cpu structure somewhere in the sugov_update_shared path,
we will likely see crashes since the memset for another CPU in the
policy is free to race with sugov_update_shared from the CPU that is
ready to go. So let's fix this now to first init all per-cpu
structures, and then add the per-cpu utilization update hooks all at
once.

Change-Id: I399e0e159b3db3ae3258843c9231f92312fe18ef
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>