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>

include/acpi/acpi_bus.h

@@ -327,6 +327,9 @@ int acpi_bus_get_private_data(acpi_handle, void **);
 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
  */