[CK] Fix gptoss sink
## Motivation
This PR removes conditional logic for handling infinity values in the
sink mechanism across multiple FMHA pipeline implementations, defaulting
sink_size to 0 and adding a constraint in the kernel selection logic.
## Technical Details
Changes:
Removed __builtin_isinf_sign(sink_v) checks and conditional
initialization of LSE accumulators across 7 pipeline files
Added default initialization (= 0) for sink_size in 4 argument structs
Added F_sink == "f" constraint to kernel compatibility checking
## Test Plan
Local test
## Test Result
passed
## Submission Checklist
- [x] Look over the contributing guidelines at
https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.
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