hexagon: flash attention rework (optimizations, accuracy improvements, etc) (#25085)

• hex-mm: fold mm quant tasks into the main matmul threads

• hex-mm: minor formatting fixes

• hex-mm: cleanup is_quant checks in dma dispatch

• hex-mm: fix dst-spad alignment

• hex-mm: move fp kernels in the hvx-mm-kernels header

• hex-mm: fuse with ADD

• hex-fa: factor out ukernels into separate headers and unify the rest

• hex-fa: move kernel-params compute into the host

• hex-fa: refactor vtcm alloc for consistency

• hex-fa: add support for FA_SELECT

• hex-fa: update tracing insrumentation to cover all functions

• hex-fa: update hvx fallback thresholds to recover t/g regressions

• hex-fa: update tracing instrumentation

• hex-fa: improved tracing with additional events

• hex-fa: optimize mask processing (fastdiv, etc)

• hex-fa: improve mask dma caching

• hmx-fa: change loop order to maximize mask cache hits

• hex-fa: remove over instrumentation

• hex-fa: breakdown QKV prep trace events

• hmx-fa: further mask proc optimizations

• hex-fa: mask broadcast is the common case, optimize for that

• hex-fa: use aligned loads where possible

• hex-fa: update loops to use uint32_t indices

• hmx-fa: fold vtcm init into q prep task

• hex-fa: update rest of the hmx funcs to use uint32_t

• hmx-fa: fold build_d into the main softmax loop

• hmx-fa: start kv dmas earlier

• hmx-fa: start mask dma a bit earlier

• hex-fa: precompute rows per task to avoid divs

• hmx-fa: specialize fa_o_store for f16 and f32

• hmx-fa: prelim support for Sinks

• hmx-fa: keep softmax accumulators in fp32

• hex-fa: add tanh_f16 and exp2_f16 and use that in FA

• hex-fa: use fp16 math in the hvx kernel

• hex-fa: avoid expensive float -> __fp16 cast for slopes and softcap

• hex-fa: replace most vec_exp_f32 with vec_exp2_f16

• hmx-fa: vectorize sinks update

• hex-fa: minor formatting

• hmx-fa: fold softcap loop into the tile load

• hmx-fa: use vectoralias to populate sinks

• hex-fa: remove redudant check

• hex-fa: fix vtcm size compute to use fp32 for accumulators

• hex-mm: fix trailing spaces

• hmx-fa: dont use -inf to init mask to avoid conversion overflows

• hex-fa: no need to explicitly guard -inf in the f16->f32 converter now

• hmx-fa: cleanup fa sinks handling

• hex-mm: fixed src2 stride handling when mm is fused with add

• hex-fa: make lto happy