hexagon: further optimization and tuning of matmul and dot kernels (llama/19407)

hexagon: further optimization and tuning of matmul and dot kernels (llama/19407)

* ggml-hexagon: implement 2x2 matmul kernel

* hexmm: implement vec_dot_rx2x2 for Q8_0 and MXFP4

* hexagon: fix editor config failures

* hexagon: refactor matmul ops to use context struct and remove wrappers

Also implement vec_dot_f16 2x2

* hexagon: refactor dyn quantizers to use mmctx

* hexagon: remove mm fastdiv from op_ctx

* hexagon: refactor matmul entry point to reduce code duplication

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Co-authored-by: Trivikram Reddy <redacted>