arm64: dts: imx: add missing cache properties

As all level 2 and level 3 caches are unified, add required
cache-unified properties to fix warnings like:

  imx8dxl-evk.dtb: l2-cache0: 'cache-unified' is a required property
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8dxl.dtsi

@@ -60,6 +60,7 @@ A35_1: cpu@1 {
 		A35_L2: l2-cache0 {
 			compatible = "cache";
 			cache-level = <2>;
+			cache-unified;
 		};
 	};
 

arch/arm64/boot/dts/freescale/imx8ulp.dtsi

@@ -52,6 +52,7 @@ A35_1: cpu@1 {
 		A35_L2: l2-cache0 {
 			compatible = "cache";
 			cache-level = <2>;
+			cache-unified;
 		};
 	};