memcg: completely decouple memcg and obj stocks

Let's completely decouple the memcg and obj per-cpu stocks.  This will
enable us to make memcg per-cpu stocks to used without disabling irqs. 
Also it will enable us to make obj stocks nmi safe independently which is
required to make kmalloc/slab safe for allocations from nmi context.

Link: https://lkml.kernel.org/r/20250506225533.2580386-4-shakeel.butt@linux.dev


Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Eric Dumaze <edumazet@google.com>
Cc: Jakub Kacinski <kuba@kernel.org>
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: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>