watchdog: dw_wdt: Convert to use watchdog infrastructure

Convert driver to use watchdog infrastructure. This includes
infrastructure support to handle watchdog keepalive if the watchdog
is running while the watchdog device is closed.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/Kconfig

@@ -350,6 +350,7 @@ config SA1100_WATCHDOG
 config DW_WATCHDOG
 	tristate "Synopsys DesignWare watchdog"
 	depends on HAS_IOMEM
+	select WATCHDOG_CORE
 	help
 	  Say Y here if to include support for the Synopsys DesignWare
 	  watchdog timer found in many chips.