xfs: extent free log intent cleanups

This series cleans up some warts in the extent freeing log intent code.
We start by acknowledging that this mechanism does not have anything to
do with the bmap code by moving it to xfs_alloc.c and giving the
function a more descriptive name.  Then we clean up the tracepoints and
the _finish_one call paths to pass the intent structure around.  This
reduces the overhead when the tracepoints are disabled and will make
things much cleaner when we start adding realtime support in the next
patch.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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