Split alloc_fixed_file_ref_node into resource generic/specific parts,
to be leveraged for fixed buffers.
Signed-off-by: NBijan Mottahedeh <bijan.mottahedeh@oracle.com>
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Reviewed-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>