arm64: dts: lg: 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:

  lg1312-ref.dtb: l2-cache0: 'cache-level' is a required property

Acked-by: Chanho Min <chanho.min@lge.com>
Link: https://lore.kernel.org/r/20230421223201.115439-1-krzysztof.kozlowski@linaro.org


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