riscv: dts: fix memory size for the SiFive HiFive Unmatched

The production version of HiFive Unmatched have 16GB memory.
Signed-off-by: Qiu Wenbo <qiuwenbo@kylinos.com.cn>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/boot/dts/sifive/hifive-unmatched-a00.dts

@@ -24,7 +24,7 @@ cpus {
 
 	memory@80000000 {
 		device_type = "memory";
-		reg = <0x0 0x80000000 0x2 0x00000000>;
+		reg = <0x0 0x80000000 0x4 0x00000000>;
 	};
 
 	soc {