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

  vexpress-v2p-ca5s.dtb: cache-controller@2c0f0000: 'cache-unified' is a required property
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230423150837.118466-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Sudeep Holla <sudeep.holla@arm.com>