PM / Sleep: Replace mutex_[un]lock(&pm_mutex) with [un]lock_system_sleep()

Using [un]lock_system_sleep() is safer than directly using mutex_[un]lock()
on 'pm_mutex', since the latter could lead to freezing failures. Hence convert
all the present users of mutex_[un]lock(&pm_mutex) to use these safe APIs
instead.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Reviewed-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/kernel/kexec.c b/kernel/kexec.c
index dc7bc08..090ee10 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -1523,7 +1523,7 @@
 
 #ifdef CONFIG_KEXEC_JUMP
 	if (kexec_image->preserve_context) {
-		mutex_lock(&pm_mutex);
+		lock_system_sleep();
 		pm_prepare_console();
 		error = freeze_processes();
 		if (error) {
@@ -1576,7 +1576,7 @@
 		thaw_processes();
  Restore_console:
 		pm_restore_console();
-		mutex_unlock(&pm_mutex);
+		unlock_system_sleep();
 	}
 #endif