ARM: dts: imx6sll: add cooling-cells for cpu-freq cooling device

Add #cooling-cells for i.MX6SLL cpu-freq cooling device usage.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6sll.dtsi

@@ -64,6 +64,7 @@ cpu0: cpu@0 {
 				198000		1175000
 			>;
 			clock-latency = <61036>; /* two CLK32 periods */
+			#cooling-cells = <2>;
 			clocks = <&clks IMX6SLL_CLK_ARM>,
 				 <&clks IMX6SLL_CLK_PLL2_PFD2>,
 				 <&clks IMX6SLL_CLK_STEP>,