[CK] Skip fp16 dropout d256 batch tests for compiler VGPR
aliasing bug (#6342)
## Summary
- Skip fp16 FMHA forward dropout tests that use the d256 tile in batch
mode, gated on compiler version
- The AMDGPU compiler miscompiles these kernels due to VGPR aliasing of
Philox RNG parameters under high register pressure (383 VGPRs)
- bf16 dropout tests are unaffected and cover the same code paths
## Root Cause
The compiler aliases `ph_seed` and `ph_head_offset` (Philox RNG state
stored in VGPRs) with other live data during the softmax main loop. This
causes corrupted `buffer_store_byte` writes for dropout randval on wave
lanes 32-63, producing NaN in output and LSE tensors.
**Conditions:** fp16 + d256 tile + dropout + batch mode + `qr` pipeline
+ gfx90a
## Changes
- `include/ck_tile/core/config.hpp`: Add
`CK_TILE_WORKAROUND_ROCM_7_12_FP16_DROPOUT_MISCOMPILE` macro
- `test/ck_tile/fmha/test_fmha_fwd.cpp`: Version-gated `GTEST_SKIP` in
`TEST_P(Dropout, ...)`
## Test plan
- [x] ROCm 7.1.1 (clang 20): 168/168 fp16 dropout tests PASS (no skip
active)
- [x] ROCm 7.12 (clang 22): 132 PASS, 36 SKIPPED, 0 FAILED
- [x] bf16 dropout tests: 168/168 PASS (unaffected by this change)
14f7834a23