io_uring: rearrange opdef flags by use pattern

Keep all flags that we use in the generic req init path close together.
That saves a load for x86 because apparently some compilers prefer
reading single bytes.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/ef03b6ce4a0c2a5234cd4037fa07e9e4902dcc9e.1740602793.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>