Bitnet: use the fused mul-silu in the FFN network (#110)

I had forgotten that build_bitnet() does not use the standerd
llm_build_ffn function, so the fused mul-silu didn't get used
for Bitnet when I added it to llm_build_ffn.

This gives us another ~1% speedup for TG-128.

Co-authored-by: Iwan Kawrakow <iwan.kawrakow@gmail.com>

Author: 2 people

src/llama.cpp

@@ -13954,12 +13954,7 @@ struct llm_build_context {
 
                 cb(cur, "ffn_gate", il);
 
-
-                // combine this with the above scale into ggml_scaled_silu
-                cur = ggml_silu(ctx0, cur);
-                cb(cur, "ffn_silu", il);
-
-                cur = ggml_mul(ctx0, cur, tmp);
+                cur = ggml_fused_mul_unary(ctx0, cur, tmp, GGML_UNARY_OP_SILU);
                 cb(cur, "ffn_gate_par", il);
 
                 cur = llm_build_norm(ctx0, cur, hparams,