cpuidle: create processor.latency_factor tunable

Start with default value of 6, so by default,
there is no functional change in this patch.

Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/processor_idle.c

@@ -94,6 +94,9 @@ module_param(bm_history, uint, 0644);
 
 static int acpi_processor_set_power_policy(struct acpi_processor *pr);
 
+#else	/* CONFIG_CPU_IDLE */
+static unsigned int latency_factor __read_mostly = 6;
+module_param(latency_factor, uint, 0644);
 #endif
 
 /*
@@ -1576,7 +1579,7 @@ static int acpi_processor_setup_cpuidle(struct acpi_processor *pr)
 
 		snprintf(state->name, CPUIDLE_NAME_LEN, "C%d", i);
 		state->exit_latency = cx->latency;
-		state->target_residency = cx->latency * 6;
+		state->target_residency = cx->latency * latency_factor;
 		state->power_usage = cx->power;
 
 		state->flags = 0;