null_blk: add blocking description and remove lightnvm

- The description of 'blocking' is missing in null_blk.txt

- The 'lightnvm' parameter has been removed in null_blk.c

This updates both in null_blk.txt.

Signed-off-by: Liu Bo <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
1 file changed