rockchip: px30: Add support for UART3 as serial output

Add the UART3 base definition for serial output, which is used on some
PX30 SoM boards.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Change-Id: I8490b15c9f129a33c01cb78bd78675014bc7b015
diff --git a/plat/rockchip/px30/px30_def.h b/plat/rockchip/px30/px30_def.h
index 9b8ccfc..283b606 100644
--- a/plat/rockchip/px30/px30_def.h
+++ b/plat/rockchip/px30/px30_def.h
@@ -54,6 +54,9 @@
 #define UART2_BASE		0xff160000
 #define UART2_SIZE		SIZE_K(64)
 
+#define UART3_BASE		0xff168000
+#define UART3_SIZE		SIZE_K(64)
+
 #define UART5_BASE		0xff178000
 #define UART5_SIZE		SIZE_K(64)