rockchip: Enable HDMI output on rk3399 board w/ HDMI

Enable config options and console setting to respective
rk3399 board for HDMI output.

Boards supported and tested on this patch are:
- NanoPc T4
- NanoPi M4
- NanoPi Neo4
- ROC-RK3399-PC
- Rock960

Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Peter Robinson <pbrobinson@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/include/configs/rock960_rk3399.h b/include/configs/rock960_rk3399.h
index 746d24c..304ad2b 100644
--- a/include/configs/rock960_rk3399.h
+++ b/include/configs/rock960_rk3399.h
@@ -6,6 +6,11 @@
 #ifndef __ROCK960_RK3399_H
 #define __ROCK960_RK3399_H
 
+#define ROCKCHIP_DEVICE_SETTINGS \
+		"stdin=serial,usbkbd\0" \
+		"stdout=serial,vidconsole\0" \
+		"stderr=serial,vidconsole\0"
+
 #include <configs/rk3399_common.h>
 
 #define CONFIG_SYS_MMC_ENV_DEV		1