ACPI / scan: Make container driver use struct acpi_scan_handler

Make the ACPI container driver use struct acpi_scan_handler for
representing the object used to initialize ACPI containers and remove
the ACPI driver structure used previously and the data structures
created by it, since in fact they were not used for any purpose.

This simplifies the code and reduces the kernel's memory footprint by
avoiding the registration of a struct device_driver object with the
driver core and creation of its sysfs directory which is unnecessary.

In addition to that, make the namespace walk callback used for
installing the notify handlers for ACPI containers more
straightforward.

This change includes fixes from Toshi Kani.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Tested-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Reviewed-by: Toshi Kani <toshi.kani@hp.com>
Tested-by: Toshi Kani <toshi.kani@hp.com>