Hexagon f16 activation ops (#29209)

* hexagon: add F16 support for activation ops (SILU/GELU/GELU_QUICK/GEGLU/SWIGLU)

Widens ggml_hexagon_supported_activations() to accept F16 (src0/dst/src1
must agree on type), and adds F16 per-thread worker functions in
act-ops.c mirroring the existing F32 workers, backed by new HVX f16
kernels (hvx_sigmoid_f16_aa, hvx_tanh_f16_aa, hvx_mul_mul_f16_aa,
hvx_min_scalar_f16 family).

SILU, GELU, GELU_QUICK, GEGLU, and SWIGLU are verified correct on-device
(QRD8850) via test-backend-ops CPU-diffed correctness tests. SWIGLU_OAI's
F16 path is code-complete and builds clean on host + all 4 DSP arch
variants (v73/v75/v79/v81), but has no F16 test-case coverage in
test-backend-ops and is therefore unverified on-device in this change.

* hex-ops: align macros

* hex-ops: minor formatting

---------

Co-authored-by: Max Krasnyansky <maxk@qti.qualcomm.com>