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

This patch document the new optional phy-supply.
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

@@ -31,6 +31,7 @@ Optional properties:
 - clocks            : a list of phandle + clock specifier pairs
 - resets            : a list of phandle + reset specifier pairs
 - target-supply     : regulator for SATA target power
+- phy-supply        : regulator for PHY power
 - phys              : reference to the SATA PHY node
 - phy-names         : must be "sata-phy"
 - ahci-supply       : regulator for AHCI controller