ggml : AVX512 gemm for Q4_0_8_8 (#9532)
* AVX512 version of ggml_gemm_q4_0_8x8_q8_0
* Remove zero vector parameter passing
* Rename functions and rearrange order of macros
* Edit commments
* style : minor adjustments
* Update x to start from 0
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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
