ggml-cpu: implement MXFP4 SIMD for s390x (#16193)

ggml-cpu: implement MXFP4 SIMD for s390x (#16193)

* ggml-cpu: impl mxfp4 s390x

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: missing s = sumf

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: fix incorrect kval_mxfp4 type

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: rework mxfp4

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: missing delta calc

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: fix typo

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: fix typo for vec_splats

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: expand to 2 blocks per loop

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: add unroll to boost perf

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: back to 1 block per loop to test perf

Signed-off-by: Aaron Teo <redacted>
* Revert "ggml-cpu: back to 1 block per loop to test perf"

This reverts commit 1fe55724e2dc295701101bf838bdd4a512237492.

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: rm unroll from single block

Signed-off-by: Aaron Teo <redacted>
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Signed-off-by: Aaron Teo <redacted>