xfs: don't use xfs_trans_free_items in the commit path

While commiting items looks very similar to freeing them on error it is
a different operation, and they will diverge a bit soon.

Split out the commit case from xfs_trans_free_items, inline it into
xfs_log_commit_cil and give it a separate trace point.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>