cpufreq: powerpc: add cpufreq transition latency for FSL e500mc SoCs

According to the data provided by HW Team, at least 12 internal platform
clock cycles are required to stabilize a DFS clock switch on FSL e500mc Socs.
This patch replaces the CPUFREQ_ETERNAL with appropriate HW clock transition
latency to make DFS governors work normally on Freescale e500mc boards.
Signed-off-by: Zhuoyu Zhang <Zhuoyu.Zhang@freescale.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/ppc-corenet-cpufreq.c

@@ -21,6 +21,7 @@
 #include <linux/of.h>
 #include <linux/slab.h>
 #include <linux/smp.h>
+#include <sysdev/fsl_soc.h>
 
 /**
  * struct cpu_data - per CPU data struct
@@ -205,7 +206,8 @@ static int corenet_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	for_each_cpu(i, per_cpu(cpu_mask, cpu))
 		per_cpu(cpu_data, i) = data;
 
-	policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
+	policy->cpuinfo.transition_latency =
+				(12 * NSEC_PER_SEC) / fsl_get_sys_freq();
 	of_node_put(np);
 
 	return 0;