io_uring: reshuffle issue_flags

Reshuffle issue flags to keep normal flags separate from the uring_cmd
ctx-setup like flags. Shift the second type to the second byte so it's
easier to add new ones in the future.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/d6e4696c883943082d248716f4cd568f37b17a74.1669821213.git.asml.silence@gmail.com


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