Add a concurrent kwarg to profiling macros. - #2201

This allows switching between concurrent and serial profiling modes. The former has less of an impact on an application's performance characteristics, but requires kernel instrumentation. The latter doesn't, and generally has less overhead.

cc @thomasfaingnaert concurrent=false is a kwarg that should be accepted by all profiling macros. I haven't seen significant improvements, but as per NVIDIA this may depend on the type of kernel:

serial: For applications which use only a single CUDA stream and therefore cannot have concurrent kernel execution, this mode can be useful as it usually (not always) incurs less profiling overhead compared to the concurrent kernel mode.

concurrent: Due to the code instrumentation, concurrent kernel mode can add significant runtime overhead if used on kernels that execute a large number of blocks and that have short execution durations.