drm/sysfs: make optional attribute groups per connector type

Split DVI-I and TV-out (which remains a group of types). As an
intermediate step, still share the attributes themselves between the
two. No user visible changes.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>