watchdog: add MT7621 watchdog support

This patch adds support for the watchdog core found on newer MediaTek Wifi
SoCs MT7621 and MT7628. There is no symbol for MT7628 as it is a subtype of
MT7620 so we depend on that instead.

Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/Kconfig

@@ -1403,6 +1403,13 @@ config RALINK_WDT
 	help
 	  Hardware driver for the Ralink SoC Watchdog Timer.
 
+config MT7621_WDT
+	tristate "Mediatek SoC watchdog"
+	select WATCHDOG_CORE
+	depends on SOC_MT7620 || SOC_MT7621
+	help
+	  Hardware driver for the Mediatek/Ralink MT7621/8 SoC Watchdog Timer.
+
 # PARISC Architecture
 
 # POWERPC Architecture