engines/io_uring: add new I/O engine for uring passthrough support

engines/io_uring: add new I/O engine for uring passthrough support

Add a new I/O engine (io_uring_cmd) for sending uring passthrough
commands. It will also use most of the existing helpers from the
I/O engine io_uring. The I/O preparation, completion, file open,
file close and post init paths are going to differ and hence
io_uring_cmd will have its own helper for them.

Add a new io_uring_cmd engine specific option to support nvme
passthrough commands. Filename name for this specific option
must specify nvme-ns generic character device (dev/ngXnY).
This provides io_uring_cmd I/O engine a bandwidth to support
various passthrough commands in future.

The engine_pos and engine_data fields in struct fio_file are
separated now. This will help I/O engine io_uring_cmd to store
specific data as well as keep track of register files.

Added a new option cmd_type. This specifies the type of uring
command to submit. Currently it only supports nvme uring command

Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
Co-authored-by: Ankit Kumar <ankit.kumar@samsung.com>
Link: https://lore.kernel.org/r/20220531133155.17493-6-ankit.kumar@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>