mm: report which part of mem is being freed on initmem case

Add the details for figuring out which parts of the kernel image is being
freed on initmem case.

Before:
   Freeing unused kernel memory: 1024K

After:
   Freeing unused kernel image (initmem) memory: 1024K

Link: https://lkml.kernel.org/r/1622706274-4533-1-git-send-email-js07.lee@samsung.comSigned-off-by: Jungseung Lee <js07.lee@samsung.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

@@ -2416,7 +2416,7 @@ static inline unsigned long free_initmem_default(int poison)
 	extern char __init_begin[], __init_end[];
 
 	return free_reserved_area(&__init_begin, &__init_end,
-				  poison, "unused kernel");
+				  poison, "unused kernel image (initmem)");
 }
 
 static inline unsigned long get_num_physpages(void)