PM / Domains: Merge measurements for PM QoS device latencies

Measure latency does by itself contribute to an increased latency, thus we
should avoid it when it isn't needed.

By merging the latency measurements for the ->save_state() and the
->stop() callbacks, we get one measurement instead of two and we get one
value to store instead of two. Let's also apply the likewise change for
the ->start() and ->restore_state() callbacks.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Lina Iyer <lina.iyer@linaro.org>
Acked-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/pm_domain.h

@@ -81,10 +81,8 @@ struct gpd_link {
 };
 
 struct gpd_timing_data {
-	s64 stop_latency_ns;
-	s64 start_latency_ns;
-	s64 save_state_latency_ns;
-	s64 restore_state_latency_ns;
+	s64 suspend_latency_ns;
+	s64 resume_latency_ns;
 	s64 effective_constraint_ns;
 	bool constraint_changed;
 	bool cached_stop_ok;