mm/damon: move migration helpers from paddr to ops-common

This patch moves the damon_pa_migrate_pages function along with its
corresponding helper functions from paddr to ops-common.  The function
prefix of "damon_pa_" was also changed to just "damon_" accordingly.

This patch will allow page migration to be available to vaddr schemes as
well as paddr schemes.

Link: https://lkml.kernel.org/r/20250709005952.17776-9-bijan311@gmail.com


Co-developed-by: Ravi Shankar Jonnalagadda <ravis.opensrc@micron.com>
Signed-off-by: Ravi Shankar Jonnalagadda <ravis.opensrc@micron.com>
Signed-off-by: Bijan Tabatabai <bijantabatab@micron.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>