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-pi-imx7d_defconfig b/configs/pico-pi-imx7d_defconfig
index 326eee5..3f75141 100644
--- a/configs/pico-pi-imx7d_defconfig
+++ b/configs/pico-pi-imx7d_defconfig
@@ -15,7 +15,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="imx7d-pico-pi"
 CONFIG_TARGET_PICO_IMX7D=y
 CONFIG_SPL_MMC=y
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_ARMV7_BOOT_SEC_DEFAULT=y
 CONFIG_IMX_RDC=y