samples: add binderfs sample program

This adds a simple sample program mounting binderfs and adding, then
removing a binder device.  Hopefully, it will be helpful to users who want
to know how binderfs is supposed to be used.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/samples/binderfs/Makefile b/samples/binderfs/Makefile
new file mode 100644
index 0000000..01ca9f2
--- /dev/null
+++ b/samples/binderfs/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_SAMPLE_ANDROID_BINDERFS) += binderfs_example.o