drm/msm: dpu: Add modeset lock checks where applicable

Add modeset lock checks to functions that could be called outside the
core atomic stack.

Changes in v2:
- None

Reviewed-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

Signed-off-by: Rob Clark <robdclark@gmail.com>