Fix build break with cuda 12.2 (#17922)
### Description
<!-- Describe your changes. -->
nvcc 12.2 crashes while building
onnxruntime/onnxruntime/contrib_ops/cuda/bert/flash_attention/flash_fwd_*
for SM<8.0. nvcc 18.8 works though. It should be a bug in nvcc 12.2.
This PR excludes building flashattention for arch < 800.
