Move the refcount update intent and intent-done pass2 commit code into
the per-item source code files and use dispatch functions to call them.
We do these one at a time because there's a lot of code to move.  No
functional changes.
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NChandan Babu R <chandanrlinux@gmail.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>