kdb: Add kdb kernel module sample

Add an example of how to add a dynamic kdb shell command via a kernel
module.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
diff --git a/samples/kdb/Makefile b/samples/kdb/Makefile
new file mode 100644
index 0000000..fbedf39
--- /dev/null
+++ b/samples/kdb/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_SAMPLE_KDB) += kdb_hello.o