drm/msm/dpu: plug-in the cdm related bits to writeback setup

drm/msm/dpu: plug-in the cdm related bits to writeback setup

To setup and enable CDM block for the writeback pipeline, lets
add the pieces together to set the active bits and the flush
bits for the CDM block.

changes in v2:
	- passed the cdm idx to update_pending_flush_cdm()
	  (have retained the R-b as its a minor change)

Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/571831/
Link: https://lore.kernel.org/r/20231212205254.12422-13-quic_abhinavk@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>