PM / OPP: Add dev_pm_opp_{un}register_get_pstate_helper()

This adds the dev_pm_opp_{un}register_get_pstate_helper() helper
routines which will be used to set the get_pstate() callback for a
device. This callback will be later called internally by the OPP core to
get performance state corresponding to an OPP.

This is required temporarily until the time we have proper DT bindings
to include the performance state information.

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

drivers/opp/opp.h

@@ -140,6 +140,7 @@ enum opp_table_access {
  * @genpd_performance_state: Device's power domain support performance state.
  * @set_opp: Platform specific set_opp callback
  * @set_opp_data: Data to be passed to set_opp callback
+ * @get_pstate: Platform specific get_pstate callback
  * @dentry:	debugfs dentry pointer of the real device directory (not links).
  * @dentry_name: Name of the real dentry.
  *
@@ -177,6 +178,7 @@ struct opp_table {
 
 	int (*set_opp)(struct dev_pm_set_opp_data *data);
 	struct dev_pm_set_opp_data *set_opp_data;
+	int (*get_pstate)(struct device *dev, unsigned long rate);
 
 #ifdef CONFIG_DEBUG_FS
 	struct dentry *dentry;