Laguna S 2.1 / Vulkan RADV native PP512/TG128

User reports Laguna S 2.1 at 21.6 t/s generation and 263 t/s prompt processing on a single Radeon 8060S iGPU in an AMD Strix Halo 128GB system. Setup is llama.cpp with the Poolside Q4_K_M quant, full offload, batch 2048, 32 threads and flash attention enabled. The figures are separate 512-token prompt and 128-token generation microbenchmarks, not one end-to-end request; the RADV arm ran 263.0 t/s prompt and 21.63 t/s generation.