Move the request list macros to the header file that defines that struct
they operate on.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220105170518.3181469-2-kbusch@kernel.org


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