Set proper nvcc threads to avoid OOM (#17419)
### Description
There are 8 cu files under [flash
attention](https://github.com/microsoft/onnxruntime/tree/main/onnxruntime/contrib_ops/cuda/bert/flash_attention)
and 4 cu files under [cutlass
fmha](https://github.com/microsoft/onnxruntime/tree/main/onnxruntime/contrib_ops/cuda/bert/cutlass_fmha)
need a lot of memory to compile.
Previously, the default value is same as parallel - number of CPU cores.
Standard_NC4as_T4_v3 has 4 CPUs and 28 GB memory, and we launched 16
nvcc threads in total (4 parallel jobs, and 4 nvcc threads per job).
Each thread might take 4 GB on average (peak is around 6GB, but threads
are not started at same time). OOM happens since 16 threads might need
close to 64 GB in worst case. When build machine has 64GB or larger
memory, OOM is rare.
Here we set a proper nvcc --threads based on available memory to avoid
OOM.
### Motivation and Context
Fix `Python Packaging Pipeline (Training Cuda 11.8)`
