ggml : add some lsx support (llama/23798)

ggml : add some lsx support (llama/23798)

* loongarch : optimize LSX fp16 load/store with native intrinsics

Use __lsx_vfcvtl_s_h and __lsx_vfcvt_h_s instead of scalar loops in
__lsx_f16x4_load and __lsx_f16x4_store.

* loongarch : add LSX implementation for q8_0 dot product

* loongarch : add LSX implementation for q6_K dot product

* loongarch : add LSX implementation for iq4_xs dot product

* Improve reduce ops when sun int16 pairs to int32