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

[remove io_sqe_rsrc_set_node substitution]
Reviewed-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NBijan Mottahedeh <bijan.mottahedeh@oracle.com>
[merge, quiesce only for files]
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>