drm/nouveau/disp/dp: explicitly control scrambling when setting pattern

TPS1/2/3 require scrambling to be disabled.  The IED scripts on earlier
boards used to handle this, but appear not to anymore.

TPS4 support will also require scrambling to remain enabled.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://gitlab.freedesktop.org/drm/nouveau/-/merge_requests/17