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/sleep.c

@@ -0,0 +1,25 @@
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#sleep */
+
+#include <linux/delay.h> /* usleep_range */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/types.h> /* atomic_t */
+
+static u32 n = 5;
+module_param(n, int, S_IRUSR | S_IWUSR);
+
+static int myinit(void)
+{
+	u32 i;
+	for (i = 0; i < n; ++i) {
+		pr_info("%d\n", i);
+		usleep_range(1000000, 1000001);
+	}
+	return 0;
+}
+
+static void myexit(void) {}
+
+module_init(myinit)
+module_exit(myexit)
+MODULE_LICENSE("GPL");