qup0 on sm6115 / sm4250 has 6 SEs, with SE4 as debug uart.
Add the debug uart node in sm6115 dtsi file.

Cc: Bjorn Andersson <andersson@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230208122718.338545-1-bhupesh.sharma@linaro.org