acpi: Export acpi_bus_type

So we can use bus_for_each_dev() and others from modules.
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20211223081620.45479-2-heikki.krogerus@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/acpi/bus.c

@@ -1043,6 +1043,7 @@ struct bus_type acpi_bus_type = {
 	.remove		= acpi_device_remove,
 	.uevent		= acpi_device_uevent,
 };
+EXPORT_SYMBOL_GPL(acpi_bus_type);
 
 /* --------------------------------------------------------------------------
                              Initialization/Cleanup