riscv: ae350: dts: Add missing "u-boot, dm-spl" for SPL config

At present the AE350 SPL defconfig is using OF_PRIOR_STAGE. The
intention was to use gdb to load device tree before running U-Boot
SPL/proper from RAM. When we switch to OF_SEPARATE we will have to
use our own DT but without "u-boot,dm-spl" in several essential
nodes, SPL does not boot.

Let's add all the required "u-boot,dm-spl" for SPL config.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>

arch/riscv/dts/ae350-u-boot.dtsi

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: (GPL-2.0 OR MIT)
+
+/ {
+	cpus {
+		u-boot,dm-spl;
+		CPU0: cpu@0 {
+			u-boot,dm-spl;
+			CPU0_intc: interrupt-controller {
+				u-boot,dm-spl;
+			};
+		};
+		CPU1: cpu@1 {
+			u-boot,dm-spl;
+			CPU1_intc: interrupt-controller {
+				u-boot,dm-spl;
+			};
+		};
+		CPU2: cpu@2 {
+			u-boot,dm-spl;
+			CPU2_intc: interrupt-controller {
+				u-boot,dm-spl;
+			};
+		};
+		CPU3: cpu@3 {
+			u-boot,dm-spl;
+			CPU3_intc: interrupt-controller {
+				u-boot,dm-spl;
+			};
+		};
+	};
+
+	memory@0 {
+		u-boot,dm-spl;
+	};
+
+	soc {
+		u-boot,dm-spl;
+
+		plic1: interrupt-controller@e6400000 {
+			u-boot,dm-spl;
+		};
+
+		plmt0@e6000000 {
+			u-boot,dm-spl;
+		};
+	};
+
+	serial0: serial@f0300000 {
+		u-boot,dm-spl;
+	};
+
+};

arch/riscv/dts/ae350_32.dts

@@ -3,6 +3,7 @@
 /dts-v1/;
 
 #include "binman.dtsi"
+#include "ae350-u-boot.dtsi"
 
 / {
 	#address-cells = <1>;

arch/riscv/dts/ae350_64.dts

@@ -3,6 +3,7 @@
 /dts-v1/;
 
 #include "binman.dtsi"
+#include "ae350-u-boot.dtsi"
 
 / {
 	#address-cells = <2>;