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/modules/hardware/cpu/amd-microcode.nix

@@ -0,0 +1,29 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+
+  ###### interface
+
+  options = {
+
+    hardware.cpu.amd.updateMicrocode = mkOption {
+      default = false;
+      type = types.bool;
+      description = ''
+        Update the CPU microcode for AMD processors.
+      '';
+    };
+
+  };
+
+
+  ###### implementation
+
+  config = mkIf config.hardware.cpu.amd.updateMicrocode {
+    # Microcode updates must be the first item prepended in the initrd
+    boot.initrd.prepend = mkOrder 1 [ "${pkgs.microcodeAmd}/amd-ucode.img" ];
+  };
+
+}