filesystem-dax: convert to dax_direct_access()

Now that a dax_device is plumbed through all dax-capable drivers we can
switch from block_device_operations to dax_operations for invoking
->direct_access.

This also lets us kill off some usages of struct blk_dax_ctl on the way
to its eventual removal.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 0d0d890..d3158e7 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -70,11 +70,13 @@
 		pgoff_t index, void *entry, bool wake_all);
 
 #ifdef CONFIG_FS_DAX
-int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
+int __dax_zero_page_range(struct block_device *bdev,
+		struct dax_device *dax_dev, sector_t sector,
 		unsigned int offset, unsigned int length);
 #else
 static inline int __dax_zero_page_range(struct block_device *bdev,
-		sector_t sector, unsigned int offset, unsigned int length)
+		struct dax_device *dax_dev, sector_t sector,
+		unsigned int offset, unsigned int length)
 {
 	return -ENXIO;
 }