drm/kms/fb: separate fbdev connector list from core drm connectors

This breaks the connection between the core drm connector list
and the fbdev connector usage, and allows them to become disjoint
in the future. It also removes the untype void* that was in the
connector struct to support this.

All connectors are added to the fbdev now but this could be
changed in the future.

Signed-off-by: Dave Airlie <airlied@redhat.com>