engines/xnvme: add support for metadata

engines/xnvme: add support for metadata

This enables support for separate metadata buffers with xnvme ioengine.
This is done by providing xnvme specific option md_per_io_size, which
for the sake of consistency is the same option used by io_uring_cmd
engine and SPDK's external ioengine.

Bump up the required xnvme support to v0.7.4

Signed-off-by: Ankit Kumar <ankit.kumar@samsung.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20240213153315.134202-3-ankit.kumar@samsung.com
Signed-off-by: Vincent Fu <vincent.fu@samsung.com>