drm/i915/hdmi: Enable pipe pixel replication for SD interlaced modes

Enable 2x pixel replication for modes the mode flag DBLCLK to double
horizontal timings and pixel clock across TMDS.

Signed-off-by: Clint Taylor <clinton.a.taylor@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>