ata: ahci_platform: add support for PHY controller regulator

The SoC R40 AHCI controller need a PHY regulator to work.
But since the PHY is embedded in the controller, we cannot do a DT node for it,
since phy-supply works only in node with a PHY compatible.
So this patch adds a way to add an optional phy-supply regulator on AHCI controller node.

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>