MAINTAINERS: add further init files to mm init block

These files comprise the bootmem info logic which is initialised on
startup and also memory tests that are run on startup and as such this
seems the most appropriate section for them.

Link: https://lkml.kernel.org/r/20250617174538.188977-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: ljskernel

MAINTAINERS

@@ -15680,8 +15680,11 @@ S:	Maintained
 F:	Documentation/core-api/boot-time-mm.rst
 F:	Documentation/core-api/kho/bindings/memblock/*
 F:	include/linux/memblock.h
+F:	mm/bootmem_info.c
 F:	mm/memblock.c
+F:	mm/memtest.c
 F:	mm/mm_init.c
+F:	mm/rodata_test.c
 F:	tools/testing/memblock/
 
 MEMORY ALLOCATION PROFILING