These are only used by the block core.  Also move the declarations to
block/blk.h.
Reported-by: NDamien Le Moal <Damien.LeMoal@wdc.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDamien Le Moal <damien.lemoal@wdc.com>
Tested-by: NDamien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>