wdt: Add MT7621 watchdog driver

This patch adds watchdog support for the Mediatek MT7621 SoC. The driver
is loosly based on the Linux kernel version.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
[fixed merge conflict in drivers/watchdog/Kconfig]
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index a911dba..4796da0 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -128,4 +128,12 @@
 config AT91_HW_WDT_TIMEOUT
 	bool "AT91 watchdog timeout specified"
 	depends on WDT_AT91
+
+config WDT_MT7621
+	bool "MediaTek MT7621 watchdog timer support"
+	depends on WDT && ARCH_MT7620
+	help
+	   Select this to enable Ralink / Mediatek watchdog timer,
+	   which can be found on some MediaTek chips.
+
 endmenu