block: move fs/block_dev.c to block/bdev.c

Move it together with the rest of the block layer.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210907141303.1371844-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/Makefile

@@ -17,7 +17,7 @@ obj-y :=	open.o read_write.o file_table.o super.o \
 		kernel_read_file.o remap_range.o
 
 ifeq ($(CONFIG_BLOCK),y)
-obj-y +=	buffer.o block_dev.o direct-io.o mpage.o
+obj-y +=	buffer.o direct-io.o mpage.o
 else
 obj-y +=	no-block.o
 endif