xfs: refactor xlog_item_is_intent now that we're done converting

Now that we've finished converting all types of log intent items to
provide an ->iop_recover function, we can convert the "is this an intent
item?" predicate to look for a non-null iop_recover pointer.

Move the predicate closer to the functions that use it.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>