vulkan: enable coopmat2 FA gqa and split_k optimizations more often (llama/12931)

vulkan: enable coopmat2 FA gqa and split_k optimizations more often (llama/12931)

The grouped query attention optmization doesn't require a power of two ratio,
the only thing relying on it was the modulo operation written as bitwise &.

split_k need not depend on gqa_ratio - enable it any time there's only one
workgroup in the X dimension. The shader gets the split index from the x coord,
and multiple workgroups in the X dimension (pre-split) indicates a larger
FA operation that wouldn't need splitting.