apple/t2: add Wi-Fi and Bluetooth firmware option

apple/t2/pkgs/brcm-firmware/fetchmacos.nix

@@ -0,0 +1,42 @@
+{
+  lib,
+  stdenvNoCC,
+  fetchFromGitHub,
+  callPackage,
+  dmg2img,
+}:
+
+let
+  macrecovery = callPackage ./macrecovery.nix { };
+in
+
+{
+  name,
+  boardId,
+  mlb,
+  osType,
+  hash,
+}:
+
+stdenvNoCC.mkDerivation {
+  name = name;
+
+  dontUnpack = true;
+
+  nativeBuildInputs = [
+    macrecovery
+    dmg2img
+  ];
+  buildPhase = ''
+    macrecovery download -o . -b ${boardId} -m ${mlb} -os ${osType}
+    dmg2img -s BaseSystem.dmg fw.img
+  '';
+
+  installPhase = ''
+    cp fw.img $out
+  '';
+
+  outputHashMode = "recursive";
+  outputHashAlgo = "sha256";
+  outputHash = hash;
+}