dt-bindings: display/msm: split dpu-qcm2290 into DPU and MDSS parts

In order to make the schema more readable, split dpu-qcm2290 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/508383/
Link: https://lore.kernel.org/r/20221024164225.3236654-11-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>