MAINTAINERS: add MEMORY HOT(UN)PLUG section and add David as reviewer

There are certainly a lot more files that partially fall into the memory
hot(un)plug category, including parts of mm/sparse.c, mm/page_isolation.c
and mm/page_alloc.c.  Let's only add what's almost completely memory
hot(un)plug related.

Add myself as reviewer so it's easier for contributors to figure out
whom to CC.

Link: https://lkml.kernel.org/r/20220610101258.75738-1-david@redhat.com
Link: https://lkml.kernel.org/r/YqlaE/LYHwB0gpaW@localhost.localdomain
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: davidhildenbrand

MAINTAINERS

@@ -12858,6 +12858,18 @@ F:	include/linux/vmalloc.h
 F:	mm/
 F:	tools/testing/selftests/vm/
 
+MEMORY HOT(UN)PLUG
+M:	David Hildenbrand <david@redhat.com>
+M:	Oscar Salvador <osalvador@suse.de>
+L:	linux-mm@kvack.org
+S:	Maintained
+F:	Documentation/admin-guide/mm/memory-hotplug.rst
+F:	Documentation/core-api/memory-hotplug.rst
+F:	drivers/base/memory.c
+F:	include/linux/memory_hotplug.h
+F:	mm/memory_hotplug.c
+F:	tools/testing/selftests/memory-hotplug/
+
 MEMORY TECHNOLOGY DEVICES (MTD)
 M:	Miquel Raynal <miquel.raynal@bootlin.com>
 M:	Richard Weinberger <richard@nod.at>