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/configs/pico-dwarf-imx6ul_defconfig b/configs/pico-dwarf-imx6ul_defconfig
index ef89b61..cf49e7c 100644
--- a/configs/pico-dwarf-imx6ul_defconfig
+++ b/configs/pico-dwarf-imx6ul_defconfig
@@ -15,7 +15,7 @@
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="imx6ul-pico-pi"
 CONFIG_SPL_MMC=y
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_SPL_LIBDISK_SUPPORT=y
 CONFIG_DISTRO_DEFAULTS=y