memblock tests: include memory_hotplug.h in mmzone.h as kernel dose

In kernel code, memory_hotplug.h is included in mmzone.h instead of in
init.h. Let's sync with kernel.

This is a preparation for move init.h in common include directory.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
CC: Mike Rapoport <rppt@kernel.org>
Link: https://lore.kernel.org/r/20240712035138.24674-1-richard.weiyang@gmail.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

tools/testing/memblock/linux/init.h

@@ -4,7 +4,6 @@
 
 #include <linux/compiler.h>
 #include <asm/export.h>
-#include <linux/memory_hotplug.h>
 
 #define __section(section)              __attribute__((__section__(section)))
 

tools/testing/memblock/linux/mmzone.h

@@ -3,6 +3,7 @@
 #define _TOOLS_MMZONE_H
 
 #include <linux/atomic.h>
+#include <linux/memory_hotplug.h>
 
 struct pglist_data *first_online_pgdat(void);
 struct pglist_data *next_online_pgdat(struct pglist_data *pgdat);