[rocm-libraries] ROCm/rocm-libraries#5504 (commit 47f86c7)

[CK Tile] Add sink token gradient support in FMHA backward pass (#5504)

## Motivation

Adds sink token support to the FMHA backward kernel (dot_do_o pipeline):

## Technical Details

- Extend BlockFmhaBwdOGradDotOPipelineProblem with LSEDataType
- Add sink_ptr/d_sink_ptr/lse_ptr/nhead to FmhaBwdOGradDotOCommonKargs
- Compute per-head sink gradient via atomic accumulation in the pipeline
- Update example runner with reference validation for sink gradient

## Test Plan

Add new test case

## Test Result

WIP

## Submission Checklist

- [ ] Look over the contributing guidelines at
https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.