[CPUFREQ] Rewrite lock in cpufreq to eliminate cpufreq/hotplug related issues

Yet another attempt to resolve cpufreq and hotplug locking issues.

Patchset has 3 patches:
* Rewrite the lock infrastructure of cpufreq using a per cpu rwsem.
* Minor restructuring of work callback in ondemand driver.
* Use the new cpufreq rwsem infrastructure in ondemand work.

This patch:

Convert policy->lock to rwsem and move it to per_cpu area.
This rwsem will protect against both changing/accessing policy
related parameters and CPU hot plug/unplug.

[malattia@linux.it: fix oops in kref_put()]
Cc: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Jones <davej@redhat.com>