cpufreq_stats: Disable cpu hotplug during stats table creation

During boot there is a possibility for two execution context to create
stats percpu variable concurrently. One called from cpufreq_stats_init
context and other as a part of policy notifier call back. This will
result in corrupted stats variable.

Disable cpu hotplug to avoid corruption.

Change-Id: Iefe2d6b370f6ec303286afc139fa9913fa9a4099
Suggested-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: Arun KS <arunks@codeaurora.org>