linuxPackages.evdi: enable parallel building

Tested at -j48.

pkgs/os-specific/linux/evdi/default.nix

···
     install -Dm755 library/libevdi.so $out/lib/libevdi.so
   '';
 
+  enableParallelBuilding = true;
+
   meta = with lib; {
     description = "Extensible Virtual Display Interface";
     maintainers = with maintainers; [ eyjhb ];