Rename SPL_WATCHDOG_SUPPORT to SPL_WATCHDOG

Rename this option so that CONFIG_IS_ENABLED can be used with it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/imx8mn_ddr4_evk_defconfig b/configs/imx8mn_ddr4_evk_defconfig
index 205757d..0c0237f 100644
--- a/configs/imx8mn_ddr4_evk_defconfig
+++ b/configs/imx8mn_ddr4_evk_defconfig
@@ -32,7 +32,7 @@
 CONFIG_SPL_BOOTROM_SUPPORT=y
 CONFIG_SPL_SEPARATE_BSS=y
 CONFIG_SPL_I2C_SUPPORT=y
-CONFIG_SPL_WATCHDOG_SUPPORT=y
+CONFIG_SPL_WATCHDOG=y
 CONFIG_SYS_PROMPT="u-boot=> "
 # CONFIG_CMD_EXPORTENV is not set
 # CONFIG_CMD_IMPORTENV is not set