dt-bindings: ata: update ahci_sunxi bindings

This patch update binding with the new R40 compatible.
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

@@ -10,6 +10,7 @@ PHYs.
 Required properties:
 - compatible        : compatible string, one of:
   - "allwinner,sun4i-a10-ahci"
+  - "allwinner,sun8i-r40-ahci"
   - "brcm,iproc-ahci"
   - "hisilicon,hisi-ahci"
   - "cavium,octeon-7130-ahci"
@@ -44,6 +45,7 @@ Required properties when using sub-nodes:
 - #address-cells    : number of cells to encode an address
 - #size-cells       : number of cells representing the size of an address
 
+For allwinner,sun8i-r40-ahci, the reset propertie must be present.
 
 Sub-nodes required properties:
 - reg		    : the port number