ACPI / bus: Move ACPI bus type registration

Move the registration of the ACPI bus type to acpi_bus_init() and
avoid using ACPI going forward if it fails (too many things depend on
the presence of the ACPI bus type).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/bus.c

@@ -1039,7 +1039,9 @@ static int __init acpi_bus_init(void)
 	 */
 	acpi_root_dir = proc_mkdir(ACPI_BUS_FILE_ROOT, NULL);
 
-	return 0;
+	result = bus_register(&acpi_bus_type);
+	if (!result)
+		return 0;
 
 	/* Mimic structured exception handling */
       error1: