Add buffer cell to scripts/yosys/synth_gates.lib

Signed-off-by: Clifford Wolf <clifford@clifford.at>

scripts/yosys/synth_gates.lib

@@ -5,6 +5,12 @@ library(gates) {
     pin(Y) { direction: output;
               function: "A'"; }
   }
+  cell(BUF) {
+    area: 4; // 2x 7404 hex inverter
+    pin(A) { direction: input; }
+    pin(Y) { direction: output;
+              function: "A"; }
+  }
   cell(NAND) {
     area: 3; // 7400 quad 2-input NAND gate
     pin(A) { direction: input; }