block: remove BLK_DEV_DAX config option

The functionality for block device DAX was already removed with commit
acc93d30d7d4 ("Revert "block: enable dax for raw block devices"")

However, we still had a config option hanging around that was always
disabled because it depended on CONFIG_BROKEN.  This config option was
introduced in commit 03cdadb04077 ("block: disable block device DAX by
default")

This change reverts that commit, removing the dead config option.

Link: http://lkml.kernel.org/r/20160729182314.6368-1-ross.zwisler@linux.intel.com
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/block_dev.c b/fs/block_dev.c
index ada42cf..2033a3f 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1275,11 +1275,7 @@
 		bdev->bd_disk = disk;
 		bdev->bd_queue = disk->queue;
 		bdev->bd_contains = bdev;
-		if (IS_ENABLED(CONFIG_BLK_DEV_DAX) &&
-		    blk_queue_dax(disk->queue))
-			bdev->bd_inode->i_flags = S_DAX;
-		else
-			bdev->bd_inode->i_flags = 0;
+		bdev->bd_inode->i_flags = 0;
 
 		if (!partno) {
 			ret = -ENXIO;