drm/exynos: dp: Disable DP scrambling

drm/exynos: dp: Disable DP scrambling

Displayport scrambling is causing screen glitches/corruption when the
device is under heavy load. This requires investigation into why it's
happening, but let's disable it until we can fix it the right way.

BUG=chrome-os-partner:11834
TEST=Tested by running 2 instances of "dd if=/dev/zero of=/dev/null"

Change-Id: I513406e1a96d762363af1ac8d831481dd877a643
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/28578
Reviewed-by: Anush Elangovan <anush@google.com>