Passing `target=...cuda_capability_86` does not imply `target=...cuda`

[jiawen]

Easier illustrated with an example than any short amount of text:

> python demosaic_generator.py -e assembly -g demosaic_generator -o cuda target=x86-64-linux-cuda-cuda_capability_86
DEBUG: target has gpu

> python demosaic_generator.py -e assembly -g demosaic_generator -o cuda target=x86-64-linux-cuda_capability_86
DEBUG: target does not have a gpu

It's not clear from the docs that for a CUDA target, one needs to pass

target=x86-64-linux-cuda-cuda_capability_86

it is not sufficient to pass

target=x86-64-linux-cuda_capability_86

Similary, for Vulkan. I had passed

target=x86-64-linux-vk_v13

and not

target=x86-64-linux-vulkan-vk_v13