modules: rename packages/kernel_modules to packages/lkmc

Then inside, split packages/lkmc into kernel_modules and userland,
to keep userland out of the kernel_modules parent path, which makes no
sense.

Copy built modules and userland to the output rootfs overlay.

Document Linux distro tradeoffs.

packages/lkmc/kernel_modules/dep.c

@@ -0,0 +1,24 @@
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#kernel-module-dependencies */
+
+#include <linux/debugfs.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+u32 lkmc_dep = 0;
+EXPORT_SYMBOL(lkmc_dep);
+static struct dentry *debugfs_file;
+
+static int myinit(void)
+{
+	debugfs_file = debugfs_create_u32("lkmc_dep", S_IRUSR | S_IWUSR, NULL, &lkmc_dep);
+	return 0;
+}
+
+static void myexit(void)
+{
+	debugfs_remove(debugfs_file);
+}
+
+module_init(myinit)
+module_exit(myexit)
+MODULE_LICENSE("GPL");