We only need this code to support scsi, ide, cciss and virtio.  And at
least for virtio it's a deprecated feature to start with.

This should shrink the kernel size for embedded device that only use,
say eMMC a bit.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>