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/common/board_r.c b/common/board_r.c
index abc31b1..ee4dced 100644
--- a/common/board_r.c
+++ b/common/board_r.c
@@ -700,7 +700,7 @@
 	stdio_init_tables,
 	initr_serial,
 	initr_announce,
-#if defined(CONFIG_WDT)
+#if CONFIG_IS_ENABLED(WDT)
 	initr_watchdog,
 #endif
 	INIT_FUNC_WATCHDOG_RESET