If "/cpus" node isn't present or "clock-latency" isn't defined we are
returning error currently. Let's return CPUFREQ_ETERNAL instead, so
that we don't fail.

Flag appropriate messages to user in such cases.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>