drm: Set the relevant infoframe field when scanning out a 3D mode

When scanning out a 3D mode on HDMI, we need to send an HDMI infoframe
with the corresponding layout to the sink.

v2: Make s3d_structure_from_display_mode() less subtle (Ville Syrjälä)

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>