FreeBSD: add missing vop_fplookup assignments

It became illegal to not have them as of
5f6df177758b9dff88e4b6069aeb2359e8b0c493 ("vfs: validate that vop
vectors provide all or none fplookup vops") upstream.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Closes #14788