io_uring: create common fixed_rsrc_ref_node handling routines

Create common routines to be used for both files/buffers registration.

[remove io_sqe_rsrc_set_node substitution]

Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>
[merge, quiesce only for files]
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>