MAINTAINERS: update SLAB ALLOCATOR maintainers

MAINTAINERS: update SLAB ALLOCATOR maintainers

With permission, reduce the number of maintainers.  Create a CREDITS entry
for Joonsoo (Pekka already has one).  Thanks for all the work!

Link: https://lkml.kernel.org/r/20250410090021.72296-3-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: Christoph Lameter (Ampere) <cl@linux.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>