Large part of bio.h, blkdev.h and genhd.h are under ifdef CONFIG_BLOCK
for no good reason.  Only stub out function that are called from
code that is not dependent on CONFIG_BLOCK and leave the harmless
other declarations around.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>