ggml-cpu: Support Q5_0 and Q5_1 on s390x (llama/15486)

ggml-cpu: Support Q5_0 and Q5_1 on s390x (llama/15486)

* ggml-cpu: initial q5_0 impl for s390x

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: updated q5_0 code for better performance

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: use optimised hsum for better performance

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: introduce q5_1 simd + refactor q5_0

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

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: q5_0 incomplete refactor + table_b2b_0 activation

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: refactor q5_1

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: q5_1 update loop unroll to 4

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: update q5_0 unroll to 4

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: update build-s390x docs

Signed-off-by: Aaron Teo <redacted>
* ggml-cpu: update unused variables q5_0

Signed-off-by: Aaron Teo <redacted>
* docs: update the last update date

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

Signed-off-by: Aaron Teo <redacted>