cpufreq: imx6q: Find max freq from frequency table itself

This is a preparatory commit to make policy->suspend_freq independent of
validation of the cpufreq table, as a later commit would update
cpufreq_generic_init() to not validate the cpufreq table any longer.

The driver already assumes the order in which the frequency table is
sorted and we can get the max frequency easily.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>