mm/damon/core: invoke kdamond_call() after merging is done if possible

mm/damon/core: invoke kdamond_call() after merging is done if possible

kdamond_call() callers may iterate the regions, so better to call it when
the number of regions is as small as possible.  It is when
kdamond_merge_regions() is finished.  Invoke it on the point.

This change is also aimed to make future changes for carrying online
parameters commit with damon_call() easier.  The commit operation should
be able to make sequence between other aggregation interval based
operations including regioins merging and aggregation reset.  Placing
damon_call() invocation after the regions merging makes the sequence
handling simpler.

Link: https://lkml.kernel.org/r/20250306175908.66300-3-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>