code refactoring for Vivado compatibility

hw/rtl/libs/VX_fixed_arbiter.sv

@@ -0,0 +1,43 @@
+`include "VX_platform.vh"
+
+`TRACING_OFF
+module VX_fixed_arbiter #(
+    parameter NUM_REQS     = 1,
+    parameter LOCK_ENABLE  = 0,
+    parameter LOG_NUM_REQS = $clog2(NUM_REQS)
+) (
+    input  wire                     clk,
+    input  wire                     reset,
+    input  wire [NUM_REQS-1:0]      requests,           
+    input  wire                     enable,
+    output wire [LOG_NUM_REQS-1:0]  grant_index,
+    output wire [NUM_REQS-1:0]      grant_onehot,   
+    output wire                     grant_valid
+  );
+
+    `UNUSED_PARAM (LOCK_ENABLE)
+    `UNUSED_VAR (clk)
+    `UNUSED_VAR (reset)
+    `UNUSED_VAR (enable)
+
+    if (NUM_REQS == 1)  begin        
+        
+        assign grant_index  = 0;
+        assign grant_onehot = requests;
+        assign grant_valid  = requests[0];
+
+    end else begin
+
+        VX_priority_encoder #(
+            .N (NUM_REQS)
+        ) tid_select (
+            .data_in   (requests),
+            .index     (grant_index),
+            .onehot    (grant_onehot),
+            .valid_out (grant_valid)
+        );
+
+    end
+    
+endmodule
+`TRACING_ON