arm: dts: rk3188: Add rk3188-u-boot.dtsi

Add U-Boot specific dtsi file for rk3188 SoC. This
would help to add U-Boot specific dts nodes, properties
which are common across rk3188.

Right now, the file is empty, will add required changes
in future patches.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>

arch/arm/dts/rk3188-radxarock-u-boot.dtsi

@@ -3,6 +3,8 @@
  * Copyright (c) 2018 Fuzhou Rockchip Electronics Co., Ltd.
  */
 
+#include "rk3188-u-boot.dtsi"
+
 &cru {
 	u-boot,dm-spl;
 };

arch/arm/dts/rk3188-u-boot.dtsi

@@ -0,0 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2019 Jagan Teki <jagan@amarulasolutions.com>
+ */