serial: Rename SERIAL_SUPPORT to SERIAL

Rename these options so that CONFIG_IS_ENABLED can be used with them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-stm32/Kconfig b/arch/arm/mach-stm32/Kconfig
index 2f1e7d3..a439dbd 100644
--- a/arch/arm/mach-stm32/Kconfig
+++ b/arch/arm/mach-stm32/Kconfig
@@ -41,7 +41,7 @@
 	select SPL_OF_TRANSLATE
 	select SPL_PINCTRL
 	select SPL_RAM
-	select SPL_SERIAL_SUPPORT
+	select SPL_SERIAL
 	select SPL_SYS_MALLOC_SIMPLE
 	select SPL_TIMER
 	select SPL_XIP_SUPPORT