libata: acpi: use acpi_device instead of acpi_handle

With commit 7b1998116bbb "ACPI / driver core: Store an ACPI device
pointer in struct acpi_dev_node", we now have direct access to the ACPI
device pointer of a physical device, eliminating the need to use
acpi_bus_get_device to get the ACPI device pointer from ACPI handle.

And there are also ACPI APIs that take acpi_device as their param, so
using those APIs could save us an acpi_bus_get_device call. To make this
happen, this patch changes ata_dev_acpi_handle to ata_dev_acpi_device.
As a result, the libata-zpodd could also be simplified a lot.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
libata: zpodd: make use of existing ACPI API to add PM notifier

Make use of the existing acpi_add/remove_pm_notifier for ZPODD wakeup
notifications.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>