NVMe: Fix IO for extended metadata formats

This fixes io submit ioctl handling when using extended metadata
formats. When these formats are used, the user provides a single virtually
contiguous buffer containing both the block and metadata interleaved,
so the metadata size needs to be added to the total length and not mapped
as a separate transfer.

The command is also driver generated, so this patch does not enforce
blk-integrity extensions provide the metadata buffer.

Reported-by: Marcin Dziegielewski <marcin.dziegielewski@intel.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>