ACPI / scan: Make scanning of fixed devices follow the general scheme

Make acpi_bus_scan_fixed() use device_attach() directly to attach
drivers, if any, to the fixed devices in analogy with how
acpi_bus_scan() works, which allows the last argument of
acpi_add_single_object() to be dropped and the manipulation of the
flags.match_driver bit to be moved to acpi_init_device_object()
and acpi_device_add_finalize().

After these changes all of the functions for the initialization
and registration of struct acpi_device objects work in the same
way for all of them.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>