arm64: dts: qcom: sm8150: add missing qcom,smmu-500 fallback

Since commit 6c84bbd1 ("dt-bindings: arm-smmu: Add generic
qcom,smmu-500 bindings") the SMMU is supposed to use qcom,smmu-500
compatible fallback.

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/20230417080939.28648-1-krzysztof.kozlowski@linaro.org