arm64: dts: allwinner: a64: add missing cache properties

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

  sun50i-a64-pine64-lts.dtb: l2-cache: 'cache-unified' is a required property

Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20230421223137.115015-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi

@@ -93,6 +93,7 @@ cpu3: cpu@3 {
 		L2: l2-cache {
 			compatible = "cache";
 			cache-level = <2>;
+			cache-unified;
 		};
 	};