drm/msm/dpu: hw_blk: make dpu_hw_blk empty opaque structure

The code does not really use dpu_hw_blk fields, so drop them, making
dpu_hw_blk empty structure.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20210515190909.1809050-5-dmitry.baryshkov@linaro.org


Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>