block: move struct request to blk-mq.h

struct request is only used by blk-mq drivers, so move it and all
related declarations to blk-mq.h.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20210920123328.1399408-18-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-crypto-fallback.c b/block/blk-crypto-fallback.c
index c322176..ec4c782 100644
--- a/block/blk-crypto-fallback.c
+++ b/block/blk-crypto-fallback.c
@@ -18,6 +18,7 @@
 #include <linux/mempool.h>
 #include <linux/module.h>
 #include <linux/random.h>
+#include <linux/scatterlist.h>
 
 #include "blk-crypto-internal.h"