MAINTAINERS: add MM subsection for the page allocator

Add a subsection for the page allocator, including compaction as it's
crucial for high-order allocations and works together with the
anti-fragmentation features.  Add reviewers (including myself) who
voluteered.

Link: https://lkml.kernel.org/r/20250410090021.72296-4-vbabka@suse.cz


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