hexagon: add HTP kernel for GGML_OP_GATED_DELTA_NET (#22837)

Implement the Gated Delta Net recurrence on HVX with:
- 4-row fused kernels for PP (prompt processing) path
- 8-row fused kernels for TG (token generation) path, reducing
  K/Q/gate vector reload overhead by 2x
- Separate PP/TG thread functions for I-cache isolation
- VTCM state scratchpad with DMA in/out for TG single-cycle access
- Vectorized gate exp via hvx_exp_f32

ggml/src/ggml-hexagon/htp/htp-ops.h

@@ -84,6 +84,7 @@ enum htp_op_code {
     HTP_OP_DIAG,
     HTP_OP_SOLVE_TRI,
     HTP_OP_L2_NORM,
+    HTP_OP_GATED_DELTA_NET,
 
     HTP_OP_INVALID
 };