dm: omap: serial: Add driver model support

Add driver model support to this driver, while retaining support for the
legacy system. Driver model serial support is enabled with CONFIG_DM_SERIAL
as usual.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@ti.com>
diff --git a/drivers/serial/Makefile b/drivers/serial/Makefile
index 17c56ea..cd87d18 100644
--- a/drivers/serial/Makefile
+++ b/drivers/serial/Makefile
@@ -41,6 +41,7 @@
 obj-$(CONFIG_ARC_SERIAL) += serial_arc.o
 obj-$(CONFIG_TEGRA_SERIAL) += serial_tegra.o
 obj-$(CONFIG_UNIPHIER_SERIAL) += serial_uniphier.o
+obj-$(CONFIG_OMAP_SERIAL) += serial_omap.o
 
 ifndef CONFIG_SPL_BUILD
 obj-$(CONFIG_USB_TTY) += usbtty.o