arm64: dts: qcom: sm6350: add debug uart

Add the necessary nodes for the debug uart on SM6350.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211007212444.328034-8-luca@z3ntu.xyz