allow changing hardware device in tests

devices/qemu.nix

@@ -0,0 +1,11 @@
+{
+  system = {
+    crossSystem = {
+      config = "mips-unknown-linux-musl";
+      gcc = {
+        abi = "32";
+        arch = "mips32";          # maybe mips_24kc-
+      };
+    };
+  };
+}