arm64: dts: mediatek: add missing cache properties

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

  mt7622-rfb1.dtb: l2-cache: 'cache-unified' is a required property

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230421223157.115367-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>