[XFS] replace some large xfs_log_priv.h macros by proper functions

... or in the case of XLOG_TIC_ADD_OPHDR remove a useless macro entirely.

SGI-PV: 968563
SGI-Modid: xfs-linux-melb:xfs-kern:29511a

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