dt-bindings: display/msm: rename mdss nodes to display-subsystem

Follow the 'generic names' rule and rename mdss nodes to
display-subsystem.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Patchwork: https://patchwork.freedesktop.org/patch/518821/
Link: https://lore.kernel.org/r/20230118041243.1720520-5-dmitry.baryshkov@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>