arm64: dts: qcom: sm6115: Add mdss_ prefix to mdss nodes

Add a mdss_ prefix to mdss nodes to keep them all near each other
when referencing them by label in device DTs.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230119101644.10711-1-konrad.dybcio@linaro.org