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/system/boot/kernel_config.nix

@@ -0,0 +1,117 @@
+{ lib, config, ... }:
+
+with lib;
+let
+  mergeFalseByDefault = locs: defs:
+    if defs == [] then abort "This case should never happen."
+    else if any (x: x == false) (getValues defs) then false
+    else true;
+
+  kernelItem = types.submodule {
+    options = {
+      tristate = mkOption {
+        type = types.enum [ "y" "m" "n" null ];
+        default = null;
+        internal = true;
+        visible = true;
+        description = ''
+          Use this field for tristate kernel options expecting a "y" or "m" or "n".
+        '';
+      };
+
+      freeform = mkOption {
+        type = types.nullOr types.str // {
+          merge = mergeEqualOption;
+        };
+        default = null;
+        example = ''MMC_BLOCK_MINORS.freeform = "32";'';
+        description = ''
+          Freeform description of a kernel configuration item value.
+        '';
+      };
+
+      optional = mkOption {
+        type = types.bool // { merge = mergeFalseByDefault; };
+        default = false;
+        description = ''
+          Whether option should generate a failure when unused.
+          Upon merging values, mandatory wins over optional.
+        '';
+      };
+    };
+  };
+
+  mkValue = with lib; val:
+  let
+    isNumber = c: elem c ["0" "1" "2" "3" "4" "5" "6" "7" "8" "9"];
+
+  in
+    if (val == "") then "\"\""
+    else if val == "y" || val == "m" || val == "n" then val
+    else if all isNumber (stringToCharacters val) then val
+    else if substring 0 2 val == "0x" then val
+    else val; # FIXME: fix quoting one day
+
+
+  # generate nix intermediate kernel config file of the form
+  #
+  #       VIRTIO_MMIO m
+  #       VIRTIO_BLK y
+  #       VIRTIO_CONSOLE n
+  #       NET_9P_VIRTIO? y
+  #
+  # Borrowed from copumpkin https://github.com/NixOS/nixpkgs/pull/12158
+  # returns a string, expr should be an attribute set
+  # Use mkValuePreprocess to preprocess option values, aka mark 'modules' as 'yes' or vice-versa
+  # use the identity if you don't want to override the configured values
+  generateNixKConf = exprs:
+  let
+    mkConfigLine = key: item:
+      let
+        val = if item.freeform != null then item.freeform else item.tristate;
+      in
+        if val == null
+          then ""
+          else if (item.optional)
+            then "${key}? ${mkValue val}\n"
+            else "${key} ${mkValue val}\n";
+
+    mkConf = cfg: concatStrings (mapAttrsToList mkConfigLine cfg);
+  in mkConf exprs;
+
+in
+{
+
+  options = {
+
+    intermediateNixConfig = mkOption {
+      readOnly = true;
+      type = types.lines;
+      example = ''
+        USB? y
+        DEBUG n
+      '';
+      description = ''
+        The result of converting the structured kernel configuration in settings
+        to an intermediate string that can be parsed by generate-config.pl to
+        answer the kernel `make defconfig`.
+      '';
+    };
+
+    settings = mkOption {
+      type = types.attrsOf kernelItem;
+      example = literalExpression '' with lib.kernel; {
+        "9P_NET" = yes;
+        USB = option yes;
+        MMC_BLOCK_MINORS = freeform "32";
+      }'';
+      description = ''
+        Structured kernel configuration.
+      '';
+    };
+  };
+
+  config = {
+    intermediateNixConfig = generateNixKConf config.settings;
+  };
+}