arm64: dts: qcom: rename mdp nodes to display-controller

Follow the schema change and rename mdp nodes to generic name
'display-controller'.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230109051402.317577-6-dmitry.baryshkov@linaro.org