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 <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

Documentation/Makefile

···
 subdir-y := accounting auxdisplay blackfin \
-	laptops pcmcia watchdog
+	laptops pcmcia

Documentation/watchdog/Makefile

···
-subdir-y := src

Documentation/watchdog/src/Makefile

···
-# List of programs to build
-hostprogs-y := watchdog-simple
-
-# Tell kbuild to always build the programs
-always := $(hostprogs-y)

Documentation/watchdog/watchdog-api.txt

···
 the watchdog is pinged within a certain time, this time is called the
 timeout or margin.  The simplest way to ping the watchdog is to write
 some data to the device.  So a very simple watchdog daemon would look
-like this source file:  see Documentation/watchdog/src/watchdog-simple.c
+like this source file:  see samples/watchdog/watchdog-simple.c
 
 A more advanced driver could for example check that a HTTP server is
 still responding before doing the write call to ping the watchdog.

Documentation/watchdog/wdt.txt

···
 Minor numbers are however allocated for it.
 
 
-Example Watchdog Driver:  see Documentation/watchdog/src/watchdog-simple.c
+Example Watchdog Driver:  see samples/watchdog/watchdog-simple.c

samples/watchdog/Makefile

···
+CC := $(CROSS_COMPILE)gcc
+PROGS := watchdog-simple
+
+all: $(PROGS)
+
+clean:
+	rm -fr $(PROGS)
+