dt-bindings: arm: atmel: add new sam9x60 reset controller binding

Update the Reset Controller's binding to add new SoC compatibility string.
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Documentation/devicetree/bindings/arm/atmel-sysregs.txt

@@ -22,6 +22,7 @@ Its subnodes can be:
 RSTC Reset Controller required properties:
 - compatible: Should be "atmel,<chip>-rstc".
   <chip> can be "at91sam9260", "at91sam9g45", "sama5d3" or "samx7"
+  it also can be "microchip,sam9x60-rstc"
 - reg: Should contain registers location and length
 - clocks: phandle to input clock.