cpufreq: Save and restore user min/max freq for hotplug

In addition to restoring the previous governor after hotplug, restore
min/max frequency set in user_policy.

This patch combines commit:
1) 026cf76c5a2b1b84cbe12b79800f97389abfd589 (android-msm-2.6.35)
   cpufreq: Save and restore min and max frequencies
2) 82a8db17421e475eb662ad83674d4f7a351bc55e (msm-3.4)
   cpufreq: Save user policy min/max instead of policy min/max during
   hotplug

And refactors it to apply cleanly onto the 3.10 kernel.

Change-Id: Id097132765a5487618ca020bae3cc9c9ea791072
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>