ata: ahci_platform: add support for AHCI controller regulator

The SoC R40 AHCI controller need a regulator to work.
So this patch add a way to add an optional regulator on AHCI controller.

Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>