ACPI: scan: Reorganize acpi_device_add()

Move the invocation of acpi_attach_data() in acpi_device_add()
into a separate function.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>