dt-bindings: ata: ahci-platform: document ahci-supply

This patch document the new optional ahci-supply.
Reviewed-by: Rob Herring <robh@kernel.org>
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>

Documentation/devicetree/bindings/ata/ahci-platform.txt

@@ -33,6 +33,7 @@ Optional properties:
 - target-supply     : regulator for SATA target power
 - phys              : reference to the SATA PHY node
 - phy-names         : must be "sata-phy"
+- ahci-supply       : regulator for AHCI controller
 - ports-implemented : Mask that indicates which ports that the HBA supports
 		      are available for software to use. Useful if PORTS_IMPL
 		      is not programmed by the BIOS, which is true with