dt-bindings: display/msm: split dpu-sc7280 into DPU and MDSS parts

In order to make the schema more readable, split dpu-sc7280 into the DPU
and MDSS parts, each one describing just a single device binding.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/508387/
Link: https://lore.kernel.org/r/20221024164225.3236654-8-dmitry.baryshkov@linaro.org


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