dt-bindings: display: msm: Add SDM670 MDSS

Add documentation for the SDM670 display subsystem, adapted from the
SDM845 and SM6125 documentation.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Richard Acayan <mailingradian@gmail.com>
Patchwork: https://patchwork.freedesktop.org/patch/562961/
Link: https://lore.kernel.org/r/20231017021805.1083350-12-mailingradian@gmail.com


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