drm/i915/hdmi: SCDC Scrambling enable without CTS mode

Setting the SCDC scrambling CTS mode causes HDMI Link Layer protocol tests
HF1-12 and HF1-13 to fail.

V2: Removed "Source Shall" entries to a new patch
V3: Rebase to drm-tip
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107895
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107896


Signed-off-by: Clint Taylor <clinton.a.taylor@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1544482374-26507-1-git-send-email-clinton.a.taylor@intel.com