memblock test: add the definition of __setup()

Commit 1e4c64b ("mm/memblock: Add "reserve_mem" to reserved named
memory at boot up") introduce usage of __setup(), which is not defined
in memblock test.

Define it in init.h to fix the build error.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Link: https://lore.kernel.org/r/20240806010319.29194-2-richard.weiyang@gmail.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Author: RichardWeiYang

tools/include/linux/init.h

@@ -34,6 +34,9 @@ struct obs_kernel_param {
 		__aligned(__alignof__(struct obs_kernel_param)) =	\
 		{ __setup_str_##unique_id, fn, early }
 
+#define __setup(str, fn)						\
+	__setup_param(str, fn, fn, 0)
+
 #define early_param(str, fn)						\
 	__setup_param(str, fn, fn, 1)