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/drivers/Makefile b/drivers/Makefile
index 6a05787..84de887 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -21,7 +21,7 @@
 obj-$(CONFIG_$(SPL_TPL_)PINCTRL) += pinctrl/
 obj-$(CONFIG_$(SPL_TPL_)RAM) += ram/
 obj-$(CONFIG_$(SPL_TPL_)RTC) += rtc/
-obj-$(CONFIG_$(SPL_TPL_)SERIAL_SUPPORT) += serial/
+obj-$(CONFIG_$(SPL_TPL_)SERIAL) += serial/
 obj-$(CONFIG_$(SPL_TPL_)SPI_SUPPORT) += spi/
 obj-$(CONFIG_$(SPL_TPL_)TIMER) += timer/
 obj-$(CONFIG_$(SPL_TPL_)VIRTIO) += virtio/