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/Makefile b/drivers/watchdog/Makefile
index 1b5f3d5..5a7fb1f 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -154,6 +154,7 @@
 obj-$(CONFIG_WATCHDOG_RTAS) += wdrtas.o
 
 # S390 Architecture
+obj-$(CONFIG_DIAG288_WATCHDOG) += diag288_wdt.o
 
 # SUPERH (sh + sh64) Architecture
 obj-$(CONFIG_SH_WDT) += shwdt.o