cpufreq: instantiate cpufreq-cpu0 as a platform_driver

As multiplatform build is being adopted by more and more ARM platforms,
initcall function should be used very carefully.  For example, when
GENERIC_CPUFREQ_CPU0 is built in the kernel, cpu0_cpufreq_driver_init()
will be called on all the platforms to initialize cpufreq-cpu0 driver.

To eliminate this undesired the effect, the patch changes cpufreq-cpu0
driver to have it instantiated as a platform_driver.  Then it will only
run on platforms that create the platform_device "cpufreq-cpu0".

Along with the change, it also changes cpu_dev to be &pdev->dev,
so that managed functions can start working, and module build gets
supported too.

The existing users of cpufreq-cpu0 driver highbank and am33xx are also
updated accordingly to adapt the changes.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
cpufreq: Revert "cpufreq: Don't use cpu removed during cpufreq_driver_unregister"

This reverts commit 956f339 "cpufreq: Don't use cpu removed during
cpufreq_driver_unregister".

With the addition of the following commit, this change/variable is not
required any more:

commit b9ba2725343ae57add3f324dfa5074167f48de96
Author: Viresh Kumar <viresh.kumar@linaro.org>
Date:   Mon Jan 14 13:23:03 2013 +0000

    cpufreq: Simplify __cpufreq_remove_dev()

[rjw: Subject and changelog]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Merge branch 'pm-cpufreq-next' into bleeding-edge

* pm-cpufreq-next:
  cpufreq: Revert "cpufreq: Don't use cpu removed during cpufreq_driver_unregister"
  cpufreq: instantiate cpufreq-cpu0 as a platform_driver