nvmet: use type-name map for ana states

Now that we have a generic type to name map for configfs, get rid of
the nvmet_ana_state_names structure and replace it with newly added
nvmet_type_name_map.

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>