mm/damon/core: split damos application logic into a new function

The DAMOS action applying function, 'damon_do_apply_schemes()', is still
long and not easy to read.  Split out the code for applying a single
action to a single region into a new function for better readability.

Link: https://lkml.kernel.org/r/20221026225943.100429-3-sj@kernel.org


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