mm: memcontrol: split out __obj_cgroup_charge()

mm: memcontrol: split out __obj_cgroup_charge()

Move the page charge and remainder calculation into its own function.  It
will make the slab stat refactor easier to follow.

Link: https://lkml.kernel.org/r/20260302195305.620713-4-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Hao Li <hao.li@linux.dev>
Cc: Johannes Weiner <jweiner@meta.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>