arm64: dts: realtek: add missing cache properties

arm64: dts: realtek: add missing cache properties

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

  rtd1293-ds418j.dtb: l2-cache: 'cache-level' is a required property
  rtd1293-ds418j.dtb: l2-cache: 'cache-unified' is a required property

Link: https://lore.kernel.org/r/20230421223151.115243-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>