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/Kconfig b/arch/arm/Kconfig
index 2006c36..69cf861 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -966,7 +966,7 @@
 	select SPL_NAND_SUPPORT if SPL_NAND_DENALI
 	select SPL_OF_CONTROL
 	select SPL_SEPARATE_BSS if TARGET_SOCFPGA_SOC64
-	select SPL_SERIAL_SUPPORT
+	select SPL_SERIAL
 	select SPL_SYSRESET
 	select SPL_WATCHDOG
 	select SUPPORT_SPL
@@ -1038,7 +1038,7 @@
 	imply SPL_LIBGENERIC_SUPPORT
 	imply SPL_MMC if MMC
 	imply SPL_POWER
-	imply SPL_SERIAL_SUPPORT
+	imply SPL_SERIAL
 	imply USB_GADGET
 
 config ARCH_U8500