dt-bindings: at_xdmac: add microchip,sam9x60-dma

Add microchip,sam9x60-dma 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/1578673089-3484-3-git-send-email-claudiu.beznea@microchip.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/dma/atmel-xdma.txt

@@ -2,7 +2,7 @@
 
 * XDMA Controller
 Required properties:
-- compatible: Should be "atmel,sama5d4-dma".
+- compatible: Should be "atmel,sama5d4-dma" or "microchip,sam9x60-dma".
 - reg: Should contain DMA registers location and length.
 - interrupts: Should contain DMA interrupt.
 - #dma-cells: Must be <1>, used to represent the number of integer cells in