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/common/spl/Kconfig b/common/spl/Kconfig
index 016eeac..c0e99ba 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -1275,7 +1275,7 @@
 	  so it can be used in compiled environment.
 endif
 
-config SPL_WATCHDOG_SUPPORT
+config SPL_WATCHDOG
 	bool "Support watchdog drivers"
 	imply SPL_WDT if !HW_WATCHDOG
 	help