drm/msm: add support to take dpu snapshot

Add the msm_disp_snapshot module which adds supports to dump dpu
registers and capture the drm atomic state which can be used in
case of error conditions.

changes in v5:
 - start storing disp_state in msm_kms instead of dpu_kms
 - get rid of MSM_DISP_SNAPSHOT_IN_* enum by simplifying the functions
 - move snprintf inside the snapshot core by using varargs
 - get rid of some stale code comments
 - allow snapshot module for non-DPU targets

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/1618606645-19695-3-git-send-email-abhinavk@codeaurora.org
Signed-off-by: Rob Clark <robdclark@chromium.org>