Start the process of making options more gfio friendly

Start the process of making options more gfio friendly

We either need to eliminate the option callbacks, or ensure that
they don't have side effects outside of touching td->o. We will
need to use &td->o as the data passed in for the callbacks, not
the full td.

Signed-off-by: Jens Axboe <axboe@kernel.dk>