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/misc/crashdump.nix

@@ -0,0 +1,76 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  crashdump = config.boot.crashDump;
+
+  kernelParams = concatStringsSep " " crashdump.kernelParams;
+
+in
+###### interface
+{
+  options = {
+    boot = {
+      crashDump = {
+        enable = mkOption {
+          type = types.bool;
+          default = false;
+          description = ''
+            If enabled, NixOS will set up a kernel that will
+            boot on crash, and leave the user in systemd rescue
+            to be able to save the crashed kernel dump at
+            /proc/vmcore.
+            It also activates the NMI watchdog.
+          '';
+        };
+        reservedMemory = mkOption {
+          default = "128M";
+          type = types.str;
+          description = ''
+            The amount of memory reserved for the crashdump kernel.
+            If you choose a too high value, dmesg will mention
+            "crashkernel reservation failed".
+          '';
+        };
+        kernelParams = mkOption {
+          type = types.listOf types.str;
+          default = [ "1" "boot.shell_on_fail" ];
+          description = ''
+            Parameters that will be passed to the kernel kexec-ed on crash.
+          '';
+        };
+      };
+    };
+  };
+
+###### implementation
+
+  config = mkIf crashdump.enable {
+    boot = {
+      postBootCommands = ''
+        echo "loading crashdump kernel...";
+        ${pkgs.kexec-tools}/sbin/kexec -p /run/current-system/kernel \
+        --initrd=/run/current-system/initrd \
+        --reset-vga --console-vga \
+        --command-line="init=$(readlink -f /run/current-system/init) irqpoll maxcpus=1 reset_devices ${kernelParams}"
+      '';
+      kernelParams = [
+       "crashkernel=${crashdump.reservedMemory}"
+       "nmi_watchdog=panic"
+       "softlockup_panic=1"
+      ];
+      kernelPatches = [ {
+        name = "crashdump-config";
+        patch = null;
+        extraConfig = ''
+                CRASH_DUMP y
+                DEBUG_INFO y
+                PROC_VMCORE y
+                LOCKUP_DETECTOR y
+                HARDLOCKUP_DETECTOR y
+              '';
+        } ];
+    };
+  };
+}