cpuidle/coupled: Add sanity check for safe_state_index

Since we are using cpuidle_driver::safe_state_index directly as the
target state index, it is better to add the sanity check at the point
of registering the driver.

Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/cpuidle/cpuidle.h b/drivers/cpuidle/cpuidle.h
index 178c5ad..f87f399 100644
--- a/drivers/cpuidle/cpuidle.h
+++ b/drivers/cpuidle/cpuidle.h
@@ -35,6 +35,7 @@
 
 #ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
 bool cpuidle_state_is_coupled(struct cpuidle_driver *drv, int state);
+int cpuidle_coupled_state_verify(struct cpuidle_driver *drv);
 int cpuidle_enter_state_coupled(struct cpuidle_device *dev,
 		struct cpuidle_driver *drv, int next_state);
 int cpuidle_coupled_register_device(struct cpuidle_device *dev);
@@ -46,6 +47,11 @@
 	return false;
 }
 
+static inline int cpuidle_coupled_state_verify(struct cpuidle_driver *drv)
+{
+	return 0;
+}
+
 static inline int cpuidle_enter_state_coupled(struct cpuidle_device *dev,
 		struct cpuidle_driver *drv, int next_state)
 {