hexagon: Flash Attention optimizations (dma, mpyacc, multi-row) and MatMul updates (#20118)

• ggml-hexagon: enhance hvx_dot_f16_f16_aa_rx4 for improved performance by expanding vector handling and optimizing accumulation

Conflicts:

ggml/src/ggml-hexagon/htp/flash-attn-ops.c

• ggml-hexagon: optimize hvx_dot_f16_f16_aa_rx4 and enhance hvx_vec_reduce_sum_f32x4 for improved performance and reduced complexity

• ggml-hexagon: add hvx_dot_f16_f16_aa_rx32 for enhanced vector processing in flash attention

Conflicts:

ggml/src/ggml-hexagon/htp/flash-attn-ops.c

• optimize hvx_dot_f16_f16_aa_rx4 and hvx_dot_f16_f16_aa_rx32 by removing unused scale parameter and improving vector accumulation

Conflicts:

ggml/src/ggml-hexagon/htp/flash-attn-ops.c

• ggml-hexagon: refactor hvx_dot_f16_f16_aa_rx4 for improved readability and return HVX_Vector for better integration

Conflicts:

ggml/src/ggml-hexagon/htp/flash-attn-ops.c

• ggml-hexagon: initialize sums variable in hvx_dot_f16_f16_aa_rx32 for clarity

• ggml-hexagon: fix compiling error

• fix hvx_dot_f16_f16_aa_rx4 to handle leftover elements correctly using masking

• refactor hvx_dot_f16_f16_aa_rx4 to accept vector and leftover element counts as parameters for improved clarity and flexibility

• wip

• fa: instrumentation and dma reordering

• hex-fa: use block-size 64 to improve DMA pipelining

• hex-fa: optimize vec-dot for v79 and above

• hex-fa: use block size 64

• hex-fa: avoid scalar fp32->fp16 conversions

• hex-fa: simplify dot_f16 functions using optimized vec_mpyacc

• hex-fa: rewrite mad_f32_f16 using hvx_vec_mpyacc

• hex-mm: use mpyacc in matmul dot functions

Co-authored-by: chraac chraac@gmail.com