bring a minimal buildroot kernel modules example to life

More importantly, to make modules_install on the Linux kernel build.

buildroot_packages/kernel_modules/buildroot_dep2.c

@@ -0,0 +1,18 @@
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#kernel-module-dependencies */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+extern u32 lkmc_dep;
+
+static int myinit(void)
+{
+	pr_info("%llu\n", (long long unsigned)lkmc_dep);
+	return 0;
+}
+
+static void myexit(void) {}
+
+module_init(myinit)
+module_exit(myexit)
+MODULE_LICENSE("GPL");