uboot: (firmwareOdroidC2/C4) don't invoke patch tool, use patches = [] instead

https://github.com/NixOS/nixpkgs/blob/master/pkgs/stdenv/generic/setup.sh#L948
this can do it nicely.

Signed-off-by: Anton Arapov <anton@deadbeef.mx>

nixos/lib/make-squashfs.nix

@@ -0,0 +1,35 @@
+{ stdenv, squashfsTools, closureInfo
+
+, # The root directory of the squashfs filesystem is filled with the
+  # closures of the Nix store paths listed here.
+  storeContents ? []
+, # Compression parameters.
+  # For zstd compression you can use "zstd -Xcompression-level 6".
+  comp ? "xz -Xdict-size 100%"
+}:
+
+stdenv.mkDerivation {
+  name = "squashfs.img";
+
+  nativeBuildInputs = [ squashfsTools ];
+
+  buildCommand =
+    ''
+      closureInfo=${closureInfo { rootPaths = storeContents; }}
+
+      # Also include a manifest of the closures in a format suitable
+      # for nix-store --load-db.
+      cp $closureInfo/registration nix-path-registration
+
+      # 64 cores on i686 does not work
+      # fails with FATAL ERROR: mangle2:: xz compress failed with error code 5
+      if ((NIX_BUILD_CORES > 48)); then
+        NIX_BUILD_CORES=48
+      fi
+
+      # Generate the squashfs image.
+      mksquashfs nix-path-registration $(cat $closureInfo/store-paths) $out \
+        -no-hardlinks -keep-as-directory -all-root -b 1048576 -comp ${comp} \
+        -processors $NIX_BUILD_CORES
+    '';
+}