iris: make resources take a ref on the screen object

iris: make resources take a ref on the screen object

Because St creates resources from a screen and attach them onto
another we need to ensure the resources associated to a screen &
bufmgr stay around until we don't need them anymore.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: <mesa-stable@lists.freedesktop.org>
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/1373
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Rafael Antognolli <rafael.antognolli@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4086>