feat(openSBI): add recipe to build OpenSBI

Signed-off-by: Diogo Costa <diogoandreveigacosta@gmail.com>

pkgs/firmware/openSBI/openSBI.nix

@@ -0,0 +1,42 @@
+# SPDX-License-Identifier: Apache-2.0
+# Copyright (c) Bao Project and Contributors. All rights reserved.
+
+{ stdenv
+, fetchFromGitHub
+, toolchain
+, openssl
+, platform
+, bao_build
+, bash
+}:
+
+stdenv.mkDerivation rec {
+    pname = "openSBI";
+    version = "bao/demo";
+
+    src = fetchFromGitHub {
+        owner = "bao-project";
+        repo = "opensbi";
+        rev = "4489876e933d8ba0d8bc6c64bae71e295d45faac"; #branch: bao/demos
+        sha256 = "sha256-k6f4/lWY/f7qqk0AFY4tdEi4cDilSv/jngaJYhKFlnY=";
+    };
+
+    nativeBuildInputs = [ toolchain openssl bash ]; #build time dependencies
+
+    postPatch = ''
+        patchShebangs ./scripts
+    '';
+
+    buildPhase = ''
+        export CROSS_COMPILE=riscv64-unknown-elf-
+        make PLATFORM=generic \
+            FW_PAYLOAD=y \
+            FW_PAYLOAD_FDT_ADDR=0x80100000
+    '';
+
+    installPhase = ''
+        mkdir -p $out/build/
+        cp -r ./build/platform/generic/firmware/fw_jump.elf $out/build/opensbi.elf
+    '';
+
+}