block/sed: Embed function data into the function sequence

By embedding the function data with the function sequence, we can
eliminate the external function data and state variable code. It also
made obvious some other small cleanups.

Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
Reviewed-by: Scott Bauer <scott.bauer@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>