blk-mq-dma: bring back p2p request flags

We only need to consider data and metadata dma mapping types separately.
The request and bio integrity payload have enough flag bits to
internally track the mapping type for each. Use these so the caller
doesn't need to track them, and provide separete request and integrity
helpers to the common code. This will make it easier to scale new
mappings, like the proposed MMIO attribute, without burdening the caller
to track such things.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>