sycl: Battlemage AOT build via spir64_gen + MMQ subgroup annotations

[aicss-genai]

Overview

Authors

• @unrahul
• @ctao456
• @malsbat
• @YuningQiu
• @vvravi1
• @zhiqitao-intel

Enables AOT builds for Intel GPUs (validated on Intel® Arc™ Pro B70, BMG-G31, Xe2-HPG):

• When GGML_SYCL_DEVICE_ARCH is set, switch to -fsycl-targets=spir64_gen with -Xsycl-target-backend="-device <arch>" and skip -ze-intel-greater-than-4GB-buffer-required (not accepted by the AOT path). Behavior is unchanged when GGML_SYCL_DEVICE_ARCH is unset.
• Adds [[intel::reqd_sub_group_size(WARP_SIZE)]] to MMQ Q4_0/Q4_1/Q5_0/Q5_1 kernel launches. WARP_SIZE=16 on Intel targets; pinning the required subgroup size is required for spir64_gen AOT correctness and documents intent on JIT.

Also adds a documentation-only update to ggml_sycl_supports_mmq (still returns false) and a note in ggml_sycl_op_mul_mat_sycl recording that fused dequant+GEMM and MMQ/DPAS were both slower than dequant+oneDNN in our experiments.

Additional information

Split from #22066 per reviewer request for independent review.

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: Yes. This work was partially produced with an agentic engineering approach: agents surface issues and explore experiments while engineers identify and reject candidates using domain knowledge. Human feedback involved.

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