watchdog: Split WDT from SPL_WDT

Use CONFIG_IS_ENABLED(WDT) to permit use of WDT in SPL without DM,
while the full U-Boot can use rich DM/DT WDT driver.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Peng Fan <Peng.Fan@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Tested-by: Heiko Schocher <hs@denx.de>
Tested-by: Suniel Mahesh <sunil.m@techveda.org>
diff --git a/include/wdt.h b/include/wdt.h
index aa77d3e..5bcff24 100644
--- a/include/wdt.h
+++ b/include/wdt.h
@@ -106,7 +106,7 @@
 	int (*expire_now)(struct udevice *dev, ulong flags);
 };
 
-#if defined(CONFIG_WDT)
+#if CONFIG_IS_ENABLED(WDT)
 #ifndef CONFIG_WATCHDOG_TIMEOUT_MSECS
 #define CONFIG_WATCHDOG_TIMEOUT_MSECS	(60 * 1000)
 #endif