rculist: add list_bidir_{del,prev}_rcu()

rculist: add list_bidir_{del,prev}_rcu()

Currently there is no primitive for retrieving the previous list member.
To do this we need a new deletion primitive that doesn't poison the prev
pointer and a corresponding retrieval helper. Note that it is not valid
to ues both list_del_rcu() and list_bidir_del_rcu() on the same list.

Link: https://lore.kernel.org/r/20241213-work-mount-rbtree-lockless-v3-4-6e3cdaf9b280@kernel.org
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>