drm/nouveau: Move the declaration of struct nouveau_conn_atom up a bit

Place the declaration of struct nouveau_conn_atom above that of
struct nouveau_connector. This commit makes no changes to the moved
block what so ever, it just moves it up a bit.

This is a preparation patch to fix some issues with connector handling
on pre nv50 displays (which do not use atomic modesetting).

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>