options: get rid of more .cb option usage we don't need

options: get rid of more .cb option usage we don't need

- The lat/bw/iops log does not need two ways of storing whether
  they are enabled or not. Just change the option to a string
  storing variant, and use the existance of a filename to see
  if it's set or not.

- The trim_percentage option need not have a callback, the
  parser knows the limits and can store it appropriately.

- The verify_offset option can express it's minimum value
  directly, it doesn't need a callback to set it on its own.

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