selftests: move watchdog tests from Documentation/watchdog

Remove watchdog-test from Makefile to move the test to selftests.

Add Makefile and .gitignore for watchdog-test. watchdog-test will
not be run as part of selftests suite and will not be included in
install targets.  It can be built separately for now.
Acked-by: NJonathan Corbet <corbet@lwn.net>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>

Documentation/watchdog/src/.gitignore

 watchdog-simple
-watchdog-test

Documentation/watchdog/src/Makefile

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

tools/testing/selftests/watchdog/.gitignore

+watchdog-test

tools/testing/selftests/watchdog/Makefile

+TEST_PROGS := watchdog-test
+
+all: $(TEST_PROGS)
+
+include ../lib.mk
+
+clean:
+	rm -fr $(TEST_PROGS)