ARM: dts: qcom: sdx55: Add Qcom SMMU-500 as the fallback for IOMMU node

SDX55 uses the Qcom version of the SMMU-500 IP. So use "qcom,smmu-500"
compatible as the fallback to the SoC specific compatible.

Cc: <stable@vger.kernel.org> # 5.12
Fixes: a2bdfdfb ("ARM: dts: qcom: sdx55: Enable ARM SMMU")
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230123131931.263024-3-manivannan.sadhasivam@linaro.org