lightnvm: pblk: implement 2.0 support

Implement 2.0 support in pblk. This includes the address formatting and
mapping paths, as well as the sysfs entries for them.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>