sycl: Update gate logic for Alchemist GPUs regarding OneDNN features. (#26635)
* feat: updated gating logic of fattn-onednn.cpp
* verified device types
* Update ggml/src/ggml-sycl/fattn-onednn.cpp
Accepted recommendations to add bmg_g31 arch.
Co-authored-by: Neo Zhang <zhang.jianyu@outlook.com>
* Improved SPDA gate, added documentation.
* Added arch var to reworked gate, fixing build errors.
* Fix trailing whitespaces.
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Co-authored-by: Neo Zhang <zhang.jianyu@outlook.com>