dt-bindings: display/msm: add core clock to the mdss bindings

Add (optional) core clock to the mdss bindings to let the MDSS driver
access hardware registers before MDP driver probes.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Patchwork: https://patchwork.freedesktop.org/patch/518816/
Link: https://lore.kernel.org/r/20230118041243.1720520-4-dmitry.baryshkov@linaro.org


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