Add CUDA architecture to CMake option when building for NVidia devices

[ndgrigorian]

Currently, DPCTL_TARGET_CUDA cmake option is binary, and doesn't allow the user to set a CUDA architecture.

This could become problematic in the future and/or for extensions which the compiler may generate code which is unusable on some architectures.

The solution is to use DPCTL_TARGET_CUDA option to allow the user to set an architecture, and if one isn't sett, to fall back to the default (sm_50 is the current default per oneAPI extension)