drm/i915: Disallow interlaced modes on g4x DP outputs

drm/i915: Disallow interlaced modes on g4x DP outputs

Looks like interlaced DP output doesn't work on g4x either. Not all
that surprising considering we already established that interlaced
DP output is busted on VLV/CHV.

Cc: stable@vger.kernel.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180613160553.11664-1-ville.syrjala@linux.intel.com
(cherry picked from commit 929168c5f3df5d9ea0ef426c33e971157d045eab)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>