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/pxm2_defconfig b/configs/pxm2_defconfig
index 44e9dc7..985e299 100644
--- a/configs/pxm2_defconfig
+++ b/configs/pxm2_defconfig
@@ -37,7 +37,7 @@
 CONFIG_SPL_NAND_BASE=y
 CONFIG_SPL_DM_SPI_FLASH=y
 CONFIG_SPL_SPI_LOAD=y
-CONFIG_SPL_WATCHDOG_SUPPORT=y
+CONFIG_SPL_WATCHDOG=y
 CONFIG_SPL_YMODEM_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="U-Boot# "