openrbg: set default based on what microcode updates are enabled

nixos-generate-config sets either of these, so lets use them

nixos/modules/services/hardware/openrgb.nix

···
 
     motherboard = mkOption {
       type = types.nullOr (types.enum [ "amd" "intel" ]);
-      default = null;
+      default = if config.hardware.cpu.intel.updateMicrocode then "intel"
+        else if config.hardware.cpu.amd.updateMicrocode then "amd"
+        else null;
+      defaultText = literalMD ''
+        if config.hardware.cpu.intel.updateMicrocode then "intel"
+        else if config.hardware.cpu.amd.updateMicrocode then "amd"
+        else null;
+      '';
       description = lib.mdDoc "CPU family of motherboard. Allows for addition motherboard i2c support.";
     };