cpufreq: Add support for per-policy driver data

Drivers supporting multiple clusters or multiple 'struct cpufreq_policy'
instances may need to keep per-policy data. If the core doesn't provide support
for that, they might do it in the most unoptimized way: 'per-cpu' data.

This patch adds another field in struct cpufreq_policy: 'driver_data'. It isn't
accessed by core and is for driver's internal use only.

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

include/linux/cpufreq.h

@@ -112,6 +112,9 @@ struct cpufreq_policy {
 	spinlock_t		transition_lock;
 	wait_queue_head_t	transition_wait;
 	struct task_struct	*transition_task; /* Task which is doing the transition */
+
+	/* For cpufreq driver's internal use */
+	void			*driver_data;
 };
 
 /* Only for ACPI */