ata: remove deprecated struct ahci_platform_data

The last user of the deprecated struct ahci_platform_data has been
cleaned up recently (SPEAr1340 got a proper PHY driver).

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>