bio_add_* cleanups

[Christoph Hellwig <hch@xxxxxx>]

Hi Jens,

this removes a bit of dead code and then further consolidates the bio_add_*
helpers.

Diffstat:
 bio.c |   89 ++++++++++++++++++++++--------------------------------------------
 blk.h |    4 --
 2 files changed, 30 insertions(+), 63 deletions(-)