ata: libata-scsi: link ata port and scsi device

There is no direct device ancestry defined between an ata_device and
its scsi device which prevents the power management code from correctly
ordering suspend and resume operations. Create such ancestry with the
ata device as the parent to ensure that the scsi device (child) is
suspended before the ata device and that resume handles the ata device
before the scsi device.

The parent-child (supplier-consumer) relationship is established between
the ata_port (parent) and the scsi device (child) with the function
device_add_link(). The parent used is not the ata_device as the PM
operations are defined per port and the status of all devices connected
through that port is controlled from the port operations.

The device link is established with the new function
ata_scsi_slave_alloc(), and this function is used to define the
->slave_alloc callback of the scsi host template of all ata drivers.

Fixes: a19a93e4

 ("scsi: core: pm: Rely on the device driver core for async power management")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Niklas Cassel <niklas.cassel@wdc.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>