Allow setting CUDA_SEPARABLE_COMPILATION property on a DIRECTORY and/or GLOBALly

The target property CUDA_SEPARABLE_COMPILATION is currently only settable for single targets. In a bigger project with 30 targets, this means that I have repeats the following line 30 times:

set_property(TARGET my_target PROPERTY CUDA_SEPARABLE_COMPILATION ON)

Please allow the target property to be set on DIRECTORY's and/or GLOBALly.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information