[CUDA] Fix SparseAttention Kernel (#20716)
### Description
Currently, there is one bool flag to indicate whether kernel is loaded.
However, there are v1 and v2 kernels, so the flag will allow only one
version of kernel loaded. We use v1 kernel for prompt and v2 kernel for
token generation, and the flag will cause issue when we want both prompt
and token generation.
This bug is found in integration test. The unit test only test one
kernel at a time so the issue was not found before.
Another possible walkaround without this fix is to set an environment
variable `ORT_DISABLE_SPARSE_ATTENTION_V1=1`
### Motivation and Context
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