rockchip: Add serial support

Add support for the Rockchip serial device using the ns16550 driver.
This uses driver model and device tree for both SPL and U-Boot proper.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/serial/Makefile b/drivers/serial/Makefile
index 1d1f036..869ea7b 100644
--- a/drivers/serial/Makefile
+++ b/drivers/serial/Makefile
@@ -40,6 +40,7 @@
 obj-$(CONFIG_BFIN_SERIAL) += serial_bfin.o
 obj-$(CONFIG_FSL_LPUART) += serial_lpuart.o
 obj-$(CONFIG_MXS_AUART) += mxs_auart.o
+obj-$(CONFIG_ROCKCHIP_SERIAL) += serial_rockchip.o
 obj-$(CONFIG_ARC_SERIAL) += serial_arc.o
 obj-$(CONFIG_TEGRA_SERIAL) += serial_tegra.o
 obj-$(CONFIG_UNIPHIER_SERIAL) += serial_uniphier.o