libnvdimm, blk: move i/o infrastructure to nd_namespace_blk

Consolidate the information for issuing i/o to a blk-namespace, and
eliminate some pointer chasing.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2 files changed