declare options.hardware.ubi unconditionally

this is so it can be defined in device modules even when
ubifs is not included in the configuration

modules/hardware.nix

@@ -13,6 +13,12 @@ in
   options = {
     boot = { };
     hardware = {
+      ubi = {
+        minIOSize = mkOption { type = types.str; };
+        logicalEraseBlockSize = mkOption { type = types.str; }; # LEB
+        physicalEraseBlockSize = mkOption { type = types.str; }; # PEB
+        maxLEBcount = mkOption { type = types.str; }; # LEB
+      };
       dts = {
         src = mkOption {
           type = types.nullOr types.path;

modules/outputs/ubifs.nix

@@ -13,13 +13,6 @@ in
     ./initramfs.nix
   ];
 
-  options.hardware.ubi = {
-    minIOSize = mkOption { type = types.str; };
-    logicalEraseBlockSize = mkOption { type = types.str; }; # LEB
-    physicalEraseBlockSize = mkOption { type = types.str; }; # PEB
-    maxLEBcount = mkOption { type = types.str; }; # LEB
-  };
-
   config = mkIf (config.rootfsType == "ubifs") {
     kernel.config = {
       MTD_UBI="y";