[GEMM] Improve performance of shape 4096x8x128x16384

[whitneywhtsang]

Currently Triton performance is ~86% of XeTLA on both default and advanced paths.

[yudongsi]

~90% of XeTLA with #2601 in CI now, WIP on more investigation and improvement.

[yudongsi]

Like #2442
Before:

After with #2646: