cudaPackages: overhaul of how we package cuda packages

There are many different versions of the `cudatoolkit` and related
cuda packages, and it can be tricky to ensure they remain compatible.

- `cudaPackages` is now a package set with `cudatoolkit`, `cudnn`, `cutensor`, `nccl`, as well as `cudatoolkit` split into smaller packages ("redist");
- expressions should now use `cudaPackages` as parameter instead of the individual cuda packages;
- `makeScope` is now used, so it is possible to use `.overrideScope'` to set e.g. a different `cudnn` version;
- `release-cuda.nix` is introduced to easily evaluate cuda packages using hydra.

pkgs/development/python-modules/libgpuarray/default.nix

@@ -9,7 +9,7 @@
 , six
 , nose
 , Mako
-, cudaSupport ? false, cudatoolkit
+, cudaSupport ? false, cudaPackages
 , openclSupport ? true, ocl-icd, clblas
 }:
 
@@ -30,7 +30,7 @@ buildPythonPackage rec {
   configurePhase = "cmakeConfigurePhase";
 
   libraryPath = lib.makeLibraryPath (
-    lib.optionals cudaSupport [ cudatoolkit.lib cudatoolkit.out ]
+    lib.optionals cudaSupport (with cudaPackages; [ cudatoolkit.lib cudatoolkit.out ])
     ++ lib.optionals openclSupport ([ clblas ] ++ lib.optional (!stdenv.isDarwin) ocl-icd)
   );