cpufreq: at32ap: add frequency table

This patch adds a dynamically calculated frequency table to the at32ap driver.
In short the architecture can scale in power of two between a maximum and
minimum frequency. Min, max, and the steps in between are added to the table.

Signed-off-by: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>