io_uring: optimise ctx flags layout

There may be different cost for reeading just one byte or more, so it's
benificial to keep ctx flag bits that we access together in a single
byte. That affected code generation of __io_cq_unlock_post_flush() and
removed one memory load.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/bbe8ca4705704690319d65e45845f9fc9d35f420.1673887636.git.asml.silence@gmail.com


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