arm64: dts: qcom: sm8450-hdk: remove useless enablement of mdss_mdp

The MDP/DPU device is not disabled by default, so there is not point in
enabling it in the board DTS file.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230531011623.3808538-4-dmitry.baryshkov@linaro.org