drm/tegra: Correct copying of waitchecks and disable them in the 'submit' IOCTL

The waitchecks along with multiple syncpoints per submit are not ready
for use yet, let's forbid them for now.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>