arm64: dts: rockchip: add missing cache properties

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

  rk3588s-khadas-edge2.dtb: l3-cache: 'cache-unified' is a dependency of 'cache-size'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230421223149.115185-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Heiko Stuebner <heiko@sntech.de>