arm64: dts: qcom: sc7180: Drop redundant disable in mdp

mdss is useless without a display controller which makes explicitly
enabling mdp redundant. Have it enabled by default to drop the extra
node for all users.

Signed-off-by: Nikita Travkin <nikita@trvn.ru>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230515093744.289045-3-nikita@trvn.ru