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-zynq/Kconfig b/arch/arm/mach-zynq/Kconfig
index 9c7c9dc..318e948 100644
--- a/arch/arm/mach-zynq/Kconfig
+++ b/arch/arm/mach-zynq/Kconfig
@@ -18,7 +18,7 @@
 config SPL_MMC
 	default y if MMC_SDHCI_ZYNQ
 
-config SPL_SERIAL_SUPPORT
+config SPL_SERIAL
 	default y
 
 config SPL_SPI_FLASH_SUPPORT