watchdog: MediaTek: add watchdog driver for MediaTek SoCs

This patch adds a common driver for the Mediatek SoC integrated
watchdog.

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Tested-by: Matthias Brugger <matthias.bgg@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index b8f2842..74738ee 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -24,3 +24,4 @@
 obj-$(CONFIG_WDT_CDNS) += cdns_wdt.o
 obj-$(CONFIG_MPC8xx_WATCHDOG) += mpc8xx_wdt.o
 obj-$(CONFIG_WDT_MT7621) += mt7621_wdt.o
+obj-$(CONFIG_WDT_MTK) += mtk_wdt.o