drm/msm/dp: add debugfs nodes for video pattern tests

Add the debugfs nodes needed for the video pattern
compliance tests to MSM DP driver.

Changes in v2: rebase on top of latest patchset of dependency

Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>