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/px30/Kconfig b/arch/arm/mach-rockchip/px30/Kconfig
index 16090f5..aa5cc47 100644
--- a/arch/arm/mach-rockchip/px30/Kconfig
+++ b/arch/arm/mach-rockchip/px30/Kconfig
@@ -36,7 +36,7 @@
 config SYS_MALLOC_F_LEN
 	default 0x400
 
-config SPL_SERIAL_SUPPORT
+config SPL_SERIAL
 	default y
 
 config TPL_LDSCRIPT