Don't malloc/memcpy ioengine_ops on td initialization

Don't malloc/memcpy ioengine_ops on td initialization

The only reason load_ioengine() needs to malloc extra space for
struct ioengine_ops and memcpy from the original ops is because td
has per-thread/process ioengine private data which is a part of
this structure.

If data (and dlhandle) are separated from struct ioengine_ops,
load_ioengine() no longer needs to malloc, as the rest of structure
fields such as function pointers and string literal are static.
Td only needs a pointer to the original ops. Also avoid memcpying
a list_head from the original ops.

This commit moves/renames data and dlhandle to struct thread_data
as thread_data::io_ops_data and thread_data::io_ops_dlhandle.
engines/*.c which access ioengine private data by dereferencing
td->io_ops->... are modified accordingly, but nothing more than that.

Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>