docs/cgroup-v1/blkio: stop abusing itemized list

Fix many formatting issues by stop (ab)using itemized lists for
everything (mostly replaced by definition lists).

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>