MAINTAINERS: add reverse mapping section

MAINTAINERS: add reverse mapping section

Separate out the reverse mapping part of memory management and assign
appropriate maintainers and reviewers.

David has long been invovled in work with the reverse mapping and
continues to do so, so is well suited to maintain this area of the kernel.

I have a lot of experience working with the anonymous reverse mapping and
continue to work in this area, and also have good knowledge of the walking
code and code related to VMAs.

This helps people identify who to ask for help, and also additionally makes
life easier in review.

Link: https://lkml.kernel.org/r/20250418150052.299220-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Acked-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>