arm64: dts: qcom: sm6115: Add smmu fallback to qcom generic compatible

Add fallback to generic qcom mmu-500 implementation.

Signed-off-by: Adam Skladowski <a39.skl@gmail.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221130200950.144618-13-a39.skl@gmail.com