ggml-cpu: add RVV vec dot kernels for quantization types (#18859)

ggml-cpu: add RVV vec dot kernels for quantization types (#18859)

* ggml-cpu: add rvv quantize_row_q8_K kernel

Co-authored-by: Rehan Qasim <redacted>
* ggml-cpu: add rvv vec_dot for iq4_nl, mxfp4, iq2_xxs

Co-authored-by: Rehan Qasim <redacted>
* ggml-cpu: add rvv vec_dot for iq4_xs, refactor

* ggml-cpu: remove ifunc for rvv vec dot

* ggml-cpu: add vec_dot for iq2_xs, iq3_xxs

Co-authored-by: Rehan Qasim <redacted>
* ggml-cpu: refactor quants.c

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Co-authored-by: taimur-10x <redacted>
Co-authored-by: Rehan Qasim <redacted>
Co-authored-by: Rehan Qasim <redacted>