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/doc/README.SPL b/doc/README.SPL
index 005f038..3fa4314 100644
--- a/doc/README.SPL
+++ b/doc/README.SPL
@@ -64,7 +64,7 @@
 CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/raw/nand_spl_load.o)
 CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o)
 CONFIG_SPL_RAM_DEVICE (common/spl/spl.c)
-CONFIG_SPL_WATCHDOG_SUPPORT (drivers/watchdog/libwatchdog.o)
+CONFIG_SPL_WATCHDOG (drivers/watchdog/libwatchdog.o)
 
 Device tree
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