MAINTAINERS: add mm THP section

As part of the ongoing efforts to sub-divide memory management
maintainership and reviewership, establish a section for Transparent Huge
Page support and add appropriate maintainers and reviewers.

[lorenzo.stoakes@oracle.com: add Dev Jain as THP reviewer]
  Link: https://lkml.kernel.org/r/327e6f2f-0f0f-48af-9ca2-3f8cadf0d8bf@lucifer.local
Link: https://lkml.kernel.org/r/20250424111632.103637-1-lorenzo.stoakes@oracle.com


Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>