nvme: update nvme lightnvm definitions

We moved channels into identify and renumbered the commands. Reflect
this in the api.
null: update documentation

Reflect the lightnvm_enable change to the documentation.
null: do not initialize LightNVM is non-mq setup

If another queueing model than blk-mq is used, LightNVM isn't supported.
Make sure to not instantiate in this case.