memcg: make PGPGIN and PGPGOUT v1 only

Currently PGPGIN and PGPGOUT are used and exposed in the memcg v1 only
code.  So, let's put them under CONFIG_MEMCG_V1.

Link: https://lkml.kernel.org/r/20240815050453.1298138-8-shakeel.butt@linux.dev


Signed-off-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>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>