[XFS] kill xfs_iocore_t

xfs_iocore_t is a structure embedded in xfs_inode. Except for one field it
just duplicates fields already in xfs_inode, and there is nothing this
abstraction buys us on XFS/Linux. This patch removes it and shrinks source
and binary size of xfs aswell as shrinking the size of xfs_inode by 60/44
bytes in debug/non-debug builds.

SGI-PV: 970852
SGI-Modid: xfs-linux-melb:xfs-kern:29754a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>