dt-bindings: atmel-matrix: add microchip,sam9x60-matrix

Add microchip,sam9x60-matrix to DT bindings documentation.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1578673089-3484-8-git-send-email-claudiu.beznea@microchip.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/mfd/atmel-matrix.txt

@@ -13,6 +13,7 @@ Required properties:
 			"atmel,at91sam9n12-matrix", "syscon"
 			"atmel,at91sam9x5-matrix", "syscon"
 			"atmel,sama5d3-matrix", "syscon"
+			"microchip,sam9x60-matrix", "syscon"
 - reg:			Contains offset/length value of the Bus Matrix
 			memory region.