dt-bindings: mtd: atmel-nand: add sam9x60 compatible

Add compatibility string for the sam9x60 nand controller.
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Documentation/devicetree/bindings/mtd/atmel-nand.txt

@@ -14,6 +14,7 @@ Required properties:
 	"atmel,at91sam9261-nand-controller"
 	"atmel,at91sam9g45-nand-controller"
 	"atmel,sama5d3-nand-controller"
+	"microchip,sam9x60-nand-controller"
 - ranges: empty ranges property to forward EBI ranges definitions.
 - #address-cells: should be set to 2.
 - #size-cells: should be set to 1.