MAINTAINERS: fixup USERFAULTFD entry

MAINTAINERS: fixup USERFAULTFD entry

Patch series "MAINTAINERS: add my isub-entries to MM part."

Following discussion at LSF/MM/BPF I'm adding execmem, secretmem and
numa memblocks sub-entries for MEMORY MANAGEMENT in MAINTAINERS.

This patch (of 4):

Change title to "MEMORY MANAGEMENT - USERFAULTFD" and make it sub-topic in
memory management and add missing include/linux/userfaultfd_k.h and
mailing list

Link: https://lkml.kernel.org/r/20250326215541.1809379-1-rppt@kernel.org
Link: https://lkml.kernel.org/r/20250326215541.1809379-2-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Dan Willaims <dan.j.williams@intel.com>
Cc: "Mike Rapoport (IBM)" <rppt@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>