drm/msm/dpu: add writeback blocks to the display snapshot

Add writeback block information while capturing the display
snapshot.

Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/483524/
Link: https://lore.kernel.org/r/1650984096-9964-18-git-send-email-quic_abhinavk@quicinc.com


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