cpufreq: dt: Add support for operating-points-v2 bindings

Support for parsing operating-points-v2 bindings is in place now, lets
modify cpufreq-dt driver to use them.

For backward compatibility we will continue to support earlier bindings.
Special handling for that is required, to make sure OPPs are initialized
for all the CPUs.

Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>