nixos/cpu/intel: allow customizing microcode package (#461556)

nixos/modules/hardware/cpu/intel-microcode.nix

@@ -4,6 +4,9 @@
   pkgs,
   ...
 }:
+let
+  cfg = config.hardware.cpu.intel;
+in
 {
   ###### interface
   options = {
@@ -15,13 +18,13 @@
         Update the CPU microcode for Intel processors.
       '';
     };
-
+    hardware.cpu.intel.microcodePackage = lib.mkPackageOption pkgs "microcode-intel" { };
   };
 
   ###### implementation
-  config = lib.mkIf config.hardware.cpu.intel.updateMicrocode {
+  config = lib.mkIf cfg.updateMicrocode {
     # Microcode updates must be the first item prepended in the initrd
-    boot.initrd.prepend = lib.mkOrder 1 [ "${pkgs.microcode-intel}/intel-ucode.img" ];
+    boot.initrd.prepend = lib.mkOrder 1 [ "${cfg.microcodePackage}/intel-ucode.img" ];
   };
 
 }