cpufreq: Add CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING cpufreq driver flag

The policy->transition_latency field is used for multiple purposes
today and its not straight forward at all. This is how it is used:

A. Set the correct transition_latency value.

B. Set it to CPUFREQ_ETERNAL because:
   1. We don't want automatic dynamic switching (with
      ondemand/conservative) to happen at all.
   2. We don't know the transition latency.

This patch handles the B.1. case in a more readable way. A new flag for
the cpufreq drivers is added to disallow use of cpufreq governors which
have dynamic_switching flag set.

All the current cpufreq drivers which are setting transition_latency
unconditionally to CPUFREQ_ETERNAL are updated to use it. They don't
need to set transition_latency anymore.

There shouldn't be any functional change after this patch.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/speedstep-smi.c

@@ -266,7 +266,6 @@ static int speedstep_cpu_init(struct cpufreq_policy *policy)
 			pr_debug("workaround worked.\n");
 	}
 
-	policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
 	return cpufreq_table_validate_and_show(policy, speedstep_freqs);
 }
 
@@ -290,6 +289,7 @@ static int speedstep_resume(struct cpufreq_policy *policy)
 
 static struct cpufreq_driver speedstep_driver = {
 	.name		= "speedstep-smi",
+	.flags		= CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING,
 	.verify		= cpufreq_generic_frequency_table_verify,
 	.target_index	= speedstep_target,
 	.init		= speedstep_cpu_init,