s390/watchdog: use watchdog API

Converted the vmwatchdog driver to use the kernel's watchdog API.

Signed-off-by: Philipp Hachtmann <phacht@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 74ec8fc..daf9441 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -1295,9 +1295,10 @@
 
 # S390 Architecture
 
-config ZVM_WATCHDOG
-	tristate "z/VM Watchdog Timer"
+config DIAG288_WATCHDOG
+	tristate "System z diag288 Watchdog"
 	depends on S390
+	select WATCHDOG_CORE
 	help
 	  IBM s/390 and zSeries machines running under z/VM 5.1 or later
 	  provide a virtual watchdog timer to their guest that cause a