cpu: sandbox: Add "u-boot, dm-pre-reloc" for all cpu nodes

To support CONFIG_DISPLAY_CPUINFO, add "u-boot,dm-pre-reloc" for
all cpu nodes in Sandbox test.dts.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>

arch/sandbox/dts/test.dts

@@ -350,14 +350,17 @@
 
 	cpu-test1 {
 		compatible = "sandbox,cpu_sandbox";
+		u-boot,dm-pre-reloc;
 	};
 
 	cpu-test2 {
 		compatible = "sandbox,cpu_sandbox";
+		u-boot,dm-pre-reloc;
 	};
 
 	cpu-test3 {
 		compatible = "sandbox,cpu_sandbox";
+		u-boot,dm-pre-reloc;
 	};
 
 	misc-test {