Add required cache-unified properties to fix warnings like:

  qcom-ipq4019-ap.dk01.1-c1.dtb: l2-cache: 'cache-unified' is a required property
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230416101134.95686-4-krzysztof.kozlowski@linaro.org