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

  berlin4ct-stb.dtb: cache: 'cache-level' is a required property
  berlin4ct-stb.dtb: cache: 'cache-unified' is a required property

Link: https://lore.kernel.org/r/20230421223145.115129-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>