dm: x86: Convert coreboot serial to use driver model

This makes use of the existing device tree node to use driver model
for the serial console.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/serial/Makefile b/drivers/serial/Makefile
index cd87d18..2c19ebc 100644
--- a/drivers/serial/Makefile
+++ b/drivers/serial/Makefile
@@ -42,6 +42,7 @@
 obj-$(CONFIG_TEGRA_SERIAL) += serial_tegra.o
 obj-$(CONFIG_UNIPHIER_SERIAL) += serial_uniphier.o
 obj-$(CONFIG_OMAP_SERIAL) += serial_omap.o
+obj-$(CONFIG_COREBOOT_SERIAL) += serial_coreboot.o
 
 ifndef CONFIG_SPL_BUILD
 obj-$(CONFIG_USB_TTY) += usbtty.o