Documentation: bindings: Add the regulator property to the sub-nodes AHCI bindings

It is now possible to use a regulator property for each port of the
AHCI controller.
Signed-off-by: NGregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: NHans de Goede <hdegoede@redhat.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

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

@@ -37,9 +37,10 @@ Required properties when using sub-nodes:
 
 
 Sub-nodes required properties:
-- reg               : the port number
-- phys              : reference to the SATA PHY node
-
+- reg		    : the port number
+And at least one of the following properties:
+- phys		    : reference to the SATA PHY node
+- target-supply    : regulator for SATA target power
 
 Examples:
         sata@ffe08000 {
@@ -68,10 +69,12 @@ With sub-nodes:
 		sata0: sata-port@0 {
 			reg = <0>;
 			phys = <&sata_phy 0>;
+			target-supply = <&reg_sata0>;
 		};
 
 		sata1: sata-port@1 {
 			reg = <1>;
 			phys = <&sata_phy 1>;
+			target-supply = <&reg_sata1>;;
 		};
 	};