[XFS] Remove the BPCSHIFT and NB* based macros from XFS.

The BPCSHIFT based macros, btoc*, ctob*, offtoc* and ctooff are either not
used or don't need to be used. The NDPP, NDPP, NBBY macros don't need to
be used but instead are replaced directly by PAGE_SIZE and PAGE_CACHE_SIZE
where appropriate. Initial patch and motivation from Nicolas Kaiser.

SGI-PV: 971186
SGI-Modid: xfs-linux-melb:xfs-kern:30096a

Signed-off-by: Tim Shimmin <tes@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>