arm: dts: rockchip: puma: move U-Boot specific bits to u-boot.dtsi

Move the U-Boot specific bits to a -u-boot.dtsi include so all the
u-boot.dtsi hierarchy is included.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/dts/rk3399-puma-ddr1600-u-boot.dtsi b/arch/arm/dts/rk3399-puma-ddr1600-u-boot.dtsi
new file mode 100644
index 0000000..be58311
--- /dev/null
+++ b/arch/arm/dts/rk3399-puma-ddr1600-u-boot.dtsi
@@ -0,0 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include "rk3399-puma-u-boot.dtsi"
+#include "rk3399-sdram-ddr3-1600.dtsi"