nvme: lightnvm: use admin queues for admin cmds

According to the Open-Channel SSD Specification, the NVMe-NVM admin
commands use vendor specific opcodes of NVMe, so use the NVMe admin
queue to dispatch these commands.

Signed-off-by: Wenwei Tao <ww.tao0320@gmail.com>
Updated by me to include set bad block table as well and also use
the admin queue for l2p len calculation.

Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>