[XFS] dinode endianess annotations

Biggest bit is duplicating the dinode structure so we have one annotated for
native endianess and one for disk endianess. The other significant change
is that xfs_xlate_dinode_core is split into one helper per direction to
allow for proper annotations, everything else is trivial.

As a sidenode splitting out the incore dinode means we can move it into
xfs_inode.h in a later patch and severely improving on the include hell in
xfs.

SGI-PV: 968563
SGI-Modid: xfs-linux-melb:xfs-kern:29476a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>