watchdog: tangier: Convert to use WDT class

Convert legacy driver to use watchdog class.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/configs/edison_defconfig b/configs/edison_defconfig
index 840c87a..4687544 100644
--- a/configs/edison_defconfig
+++ b/configs/edison_defconfig
@@ -39,5 +39,7 @@
 CONFIG_USB_GADGET_PRODUCT_NUM=0x0a99
 CONFIG_USB_GADGET_DOWNLOAD=y
 # CONFIG_USB_HOST_ETHER is not set
+CONFIG_WDT=y
+CONFIG_WDT_TANGIER=y
 CONFIG_FAT_WRITE=y
 CONFIG_SHA1=y