Make CUDA and ROCm architecture conditional (#27185)

* Make CUDA and ROCm architecture conditional

fixes #14337

The variant to specify which architecture to use
for CUDA and ROCm are now conditional on +cuda and
+rocm respectively.

* cp2k: make all CUDA related variants conditional on +cuda

lib/spack/spack/build_systems/cuda.py

@@ -35,7 +35,8 @@ class CudaPackage(PackageBase):
 
     variant('cuda_arch',
             description='CUDA architecture',
-            values=spack.variant.any_combination_of(*cuda_arch_values))
+            values=spack.variant.any_combination_of(*cuda_arch_values),
+            when='+cuda')
 
     # https://docs.nvidia.com/cuda/cuda-compiler-driver-nvcc/index.html#nvcc-examples
     # https://llvm.org/docs/CompileCudaWithLLVM.html#compiling-cuda-code

lib/spack/spack/build_systems/rocm.py

@@ -100,7 +100,8 @@ class ROCmPackage(PackageBase):
     # possible amd gpu targets for rocm builds
     variant('amdgpu_target',
             description='AMD GPU architecture',
-            values=spack.variant.any_combination_of(*amdgpu_targets))
+            values=spack.variant.any_combination_of(*amdgpu_targets),
+            when='+rocm')
 
     depends_on('llvm-amdgpu', when='+rocm')
     depends_on('hsa-rocr-dev', when='+rocm')