nvme: add helper nvme_map_len()

The helper returns the number of bytes that need to be mapped
using PRPs/SGL entries.

Signed-off-by: Ming Lin <ming.l@ssi.samsung.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
2 files changed