icestorm: move the directory to pkgs/development/embedded/fpga/

pkgs/top-level/all-packages.nix

···
   iaca_3_0 = callPackage ../development/tools/iaca/3.0.nix { };
   iaca = iaca_3_0;
 
-  icestorm = callPackage ../development/tools/icestorm { };
+  icestorm = callPackage ../development/embedded/fpga/icestorm { };
 
   icmake = callPackage ../development/tools/build-managers/icmake { };