dt-bindings: clk: at91: add bindings for SAM9X60's slow clock controller

Add bindings for SAM9X60's slow clock controller.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Documentation/devicetree/bindings/clock/at91-clock.txt

@@ -9,10 +9,11 @@ Slow Clock controller:
 Required properties:
 - compatible : shall be one of the following:
 	"atmel,at91sam9x5-sckc",
-	"atmel,sama5d3-sckc" or
-	"atmel,sama5d4-sckc":
+	"atmel,sama5d3-sckc",
+	"atmel,sama5d4-sckc" or
+	"microchip,sam9x60-sckc":
 		at91 SCKC (Slow Clock Controller)
-- #clock-cells : shall be 0.
+- #clock-cells : shall be 1 for "microchip,sam9x60-sckc" otherwise shall be 0.
 - clocks : shall be the input parent clock phandle for the clock.
 
 Optional properties: