block: move elevator.h to block/

Except for the features passed to blk_queue_required_elevator_features,
elevator.h is only needed internally to the block layer.  Move the
ELEVATOR_F_* definitions to blkdev.h, and the move elevator.h to
block/, dropping all the spurious includes outside of that.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20210920123328.1399408-13-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index a0ffbab..53dafc4 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -9,12 +9,12 @@
 #include <linux/kernel.h>
 #include <linux/blkdev.h>
 #include <linux/blk-mq.h>
-#include <linux/elevator.h>
 #include <linux/module.h>
 #include <linux/sbitmap.h>
 
 #include <trace/events/block.h>
 
+#include "elevator.h"
 #include "blk.h"
 #include "blk-mq.h"
 #include "blk-mq-debugfs.h"