samples: move watchdog example code from Documentation

Move watchdog examples to samples and remove it from Documentation
Makefile. Create a new Makefile to build watchdog. It can be built
from top level directory or from watchdog directory:

Run make -C samples/watchdog or cd samples/watchdog; make

Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
diff --git a/samples/watchdog/Makefile b/samples/watchdog/Makefile
new file mode 100644
index 0000000..9b53d89
--- /dev/null
+++ b/samples/watchdog/Makefile
@@ -0,0 +1,8 @@
+CC := $(CROSS_COMPILE)gcc
+PROGS := watchdog-simple
+
+all: $(PROGS)
+
+clean:
+	rm -fr $(PROGS)
+