drm/msm/dp: remove mode hard-coding in case of DP CTS

No need to fix the number of resolutions to one during the video
pattern CTS test. The userspace test client will handle both
the hotplug as well as picking the right resolution for the test.

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>