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-rockchip/rk3188/Kconfig b/arch/arm/mach-rockchip/rk3188/Kconfig
index e24e68e..9a76490 100644
--- a/arch/arm/mach-rockchip/rk3188/Kconfig
+++ b/arch/arm/mach-rockchip/rk3188/Kconfig
@@ -24,7 +24,7 @@
 config SPL_LIBGENERIC_SUPPORT
 	default y
 
-config SPL_SERIAL_SUPPORT
+config SPL_SERIAL
 	default y
 
 config TPL_LIBCOMMON_SUPPORT