ARM: dts: imx6dl: Add missing cooling device properties for CPUs

The cooling device properties "#cooling-cells" should either be present
for all the CPUs of a cluster or none. If these are present only for a
subset of CPUs of a cluster then things will start falling apart as soon
as the CPUs are brought online in a different order. For example, this
will happen because the operating system looks for such properties in the
CPU node it is trying to bring up, so that it can register a cooling
device.

Add such missing properties.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6dl.dtsi

@@ -64,6 +64,7 @@ cpu@1 {
 				396000	1175000
 			>;
 			clock-latency = <61036>; /* two CLK32 periods */
+			#cooling-cells = <2>;
 			clocks = <&clks IMX6QDL_CLK_ARM>,
 				 <&clks IMX6QDL_CLK_PLL2_PFD2_396M>,
 				 <&clks IMX6QDL_CLK_STEP>,