riscv: sifive: fu540: Use OTP DM driver for serial environment variable

Use the OTP DM driver to set the serial environment variable.

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/arch/riscv/dts/fu540-c000-u-boot.dtsi b/arch/riscv/dts/fu540-c000-u-boot.dtsi
new file mode 100644
index 0000000..db55773
--- /dev/null
+++ b/arch/riscv/dts/fu540-c000-u-boot.dtsi
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: (GPL-2.0 OR MIT)
+/*
+ * (C) Copyright 2019 SiFive, Inc
+ */
+
+/ {
+	soc {
+		otp: otp@10070000 {
+			compatible = "sifive,fu540-c000-otp";
+			reg = <0x0 0x10070000 0x0 0x0FFF>;
+			fuse-count = <0x1000>;
+		};
+	};
+};