memblock tests: fix undefined reference to `panic'

commit e96c6b8f ("memblock: report failures when memblock_can_resize
is not set") introduced the usage of panic, which is not defined in
memblock test.

Let's define it directly in panic.h to fix it.
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
CC: Song Shuai <songshuaishuai@tinylab.org>
CC: Mike Rapoport <rppt@kernel.org>
Link: https://lore.kernel.org/r/20240402132701.29744-3-richard.weiyang@gmail.comSigned-off-by: Mike Rapoport (IBM) <rppt@kernel.org>

tools/include/linux/kernel.h

@@ -8,6 +8,7 @@
 #include <linux/build_bug.h>
 #include <linux/compiler.h>
 #include <linux/math.h>
+#include <linux/panic.h>
 #include <endian.h>
 #include <byteswap.h>
 

tools/include/linux/panic.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _TOOLS_LINUX_PANIC_H
+#define _TOOLS_LINUX_PANIC_H
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static inline void panic(const char *fmt, ...)
+{
+	va_list argp;
+
+	va_start(argp, fmt);
+	vfprintf(stderr, fmt, argp);
+	va_end(argp);
+	exit(-1);
+}
+
+#endif