xfs: factor log item initialisation

Each log item type does manual initialisation of the log item.
Delayed logging introduces new fields that need initialisation, so
factor all the open coded initialisation into a common function
first.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --cc fs/xfs/quota/xfs_dquot_item.c
Simple merge

diff --cc fs/xfs/xfs_buf_item.c
Simple merge

diff --cc fs/xfs/xfs_extfree_item.c
Simple merge

diff --cc fs/xfs/xfs_inode_item.c
Simple merge

diff --cc fs/xfs/xfs_log.c
Simple merge

diff --cc fs/xfs/xfs_log.h
Simple merge