ftrace: Add sample module that uses register_ftrace_direct()

Add a sample module that shows a simple use case for
regsiter_ftrace_direct(), and how to use it.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
diff --git a/samples/Makefile b/samples/Makefile
index 7d6e4ca..cd496d6 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -17,6 +17,7 @@
 subdir-$(CONFIG_SAMPLE_SECCOMP)		+= seccomp
 obj-$(CONFIG_SAMPLE_TRACE_EVENTS)	+= trace_events/
 obj-$(CONFIG_SAMPLE_TRACE_PRINTK)	+= trace_printk/
+obj-$(CONFIG_SAMPLE_FTRACE_DIRECT)	+= ftrace/
 obj-$(CONFIG_VIDEO_PCI_SKELETON)	+= v4l/
 obj-y					+= vfio-mdev/
 subdir-$(CONFIG_SAMPLE_VFS)		+= vfs