cpufreq: cpufreq-dt: extend with platform_data

This commit extends the cpufreq-dt driver to take a platform_data
structure. This structure is for now used to tell the cpufreq-dt
driver the layout of the clocks on the platform, i.e whether all CPUs
share the same clock or whether each CPU has a separate clock.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>