ACPI: introduce notifier change to avoid duplicates

The battery driver already registers notification handler.
To avoid registering notification handler again,
introduce a notifier chain in global system notifier handler
and use it in dock driver.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index a5ac0bc..f74f882 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -327,6 +327,9 @@
 extern int acpi_notifier_call_chain(struct acpi_device *, u32, u32);
 extern int register_acpi_notifier(struct notifier_block *);
 extern int unregister_acpi_notifier(struct notifier_block *);
+
+extern int register_acpi_bus_notifier(struct notifier_block *nb);
+extern void unregister_acpi_bus_notifier(struct notifier_block *nb);
 /*
  * External Functions
  */