mm/damon/modules: deduplicate init steps for DAMON context setup

DAMON_RECLAIM and DAMON_LRU_SORT has duplicated code for DAMON context and
target initializations.  Deduplicate the part by implementing a function
for the initialization in 'modules-common.c' and using it.

Link: https://lkml.kernel.org/r/20221026225943.100429-12-sj@kernel.org


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