tools/testing: abstract two init.h into common include directory

Currently we have two test suits define its own init.h. This is a little
redundant.

Let's create a init.h in common include directory and merge these two
into it.

Signed-off-by: Wei Yang <[e-mail]>
CC: Mike Rapoport <[e-mail]>
CC: Liam R. Howlett <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mike Rapoport (Microsoft) <[e-mail]>

tools/include/linux/compiler.h

···
 # define unlikely(x)		__builtin_expect(!!(x), 0)
 #endif
 
-#ifndef __init
-# define __init
-#endif
-
 #include <linux/types.h>
 
 /*

tools/testing/memblock/linux/init.h tools/include/linux/init.h

···
 /* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _LINUX_INIT_H
-#define _LINUX_INIT_H
+#ifndef _TOOLS_LINUX_INIT_H_
+#define _TOOLS_LINUX_INIT_H_
 
 #include <linux/compiler.h>
+
+#ifndef __init
+# define __init
+#endif
+
+#ifndef __exit
+# define __exit
+#endif
 
 #define __section(section)              __attribute__((__section__(section)))
 
···
 #define early_param(str, fn)						\
 	__setup_param(str, fn, fn, 1)
 
-#endif
+#endif /*  _TOOLS_LINUX_INIT_H_ */

tools/testing/radix-tree/linux/init.h

···
-#define __init
-#define __exit

tools/testing/radix-tree/maple.c

···
 #include "test.h"
 #include <stdlib.h>
 #include <time.h>
-#include "linux/init.h"
+#include <linux/init.h>
 
 #define module_init(x)
 #define module_exit(x)