mm: memcg: guard memcg1-specific members of struct mem_cgroup_per_node

Put memcg1-specific members of struct mem_cgroup_per_node under the
CONFIG_MEMCG_V1 config option.

Link: https://lkml.kernel.org/r/20240628210317.272856-8-roman.gushchin@linux.dev


Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>