mm/damon/sysfs: reuse damon_set_regions() for regions setting

'damon_set_regions()' is general enough so that it can also be used for
only creating regions.  This commit makes DAMON sysfs interface to reuse
the function rather keeping two implementations for a same purpose.

Link: https://lkml.kernel.org/r/20220429160606.127307-9-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>