ARM: dts: en7523: 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:

  en7523-evb.dtb: l2-cache0: 'cache-level' is a required property
  en7523-evb.dtb: l2-cache0: 'cache-unified' is a required property

Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Link: https://lore.kernel.org/r/20230423150824.118430-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>