kernel/reboot: Add do_kernel_power_off()

Add do_kernel_power_off() helper that will remove open-coded pm_power_off
invocations from the architecture code. This is the first step on the way
to remove the global pm_power_off variable, which will allow us to
implement consistent power-off chaining support.
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/reboot.h

@@ -63,6 +63,8 @@ extern void machine_shutdown(void);
 struct pt_regs;
 extern void machine_crash_shutdown(struct pt_regs *);
 
+void do_kernel_power_off(void);
+
 /*
  * sys-off handler API.
  */

kernel/reboot.c

@@ -504,6 +504,19 @@ static void do_kernel_power_off_prepare(void)
 	blocking_notifier_call_chain(&power_off_prep_handler_list, 0, NULL);
 }
 
+/**
+ *	do_kernel_power_off - Execute kernel power-off handler call chain
+ *
+ *	Expected to be called as last step of the power-off sequence.
+ *
+ *	Powers off the system immediately if a power-off handler function has
+ *	been registered. Otherwise does nothing.
+ */
+void do_kernel_power_off(void)
+{
+	atomic_notifier_call_chain(&power_off_handler_list, 0, NULL);
+}
+
 /**
  *	kernel_power_off - power_off the system
  *