dt-bindings: display: msm: sm8350-mdss: Describe the CPU-CFG icc path

There's a separate path that allows register access from CPUSS.
Describe it.

Signed-off-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/641464/
Link: https://lore.kernel.org/r/20250306-topic-dt_bindings_fixups-v1-2-0c84aceb0ef9@oss.qualcomm.com


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>