drm/msm: make msm_disp_state transient data struct

drm/msm: make msm_disp_state transient data struct

Instead of allocating snapshotting structure at the driver probe time
and later handling concurrent access, actual state, etc, make
msm_disp_state transient struct. Allocate one when snapshotting happens
and free it after coredump data is read by userspace.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Link: https://lore.kernel.org/r/20210427001828.2375555-3-dmitry.baryshkov@linaro.org
Signed-off-by: Rob Clark <robdclark@chromium.org>