Use skid buffer on CSR IO bus to stop backpressure delay propagation into csr_unit

hw/rtl/libs/VX_elastic_buffer.v

@@ -3,28 +3,35 @@
 module VX_elastic_buffer #(
     parameter DATAW    = 1,
     parameter SIZE     = 2,
-    parameter BUFFERED = 0
+    parameter BUFFERED = 0,
+    parameter FASTRAM  = 0
 ) ( 
     input  wire             clk,
     input  wire             reset,
+
     input  wire             valid_in,
     output wire             ready_in,        
     input  wire [DATAW-1:0] data_in,
+    
     output wire [DATAW-1:0] data_out,
     input  wire             ready_out,
     output wire             valid_out
 ); 
     wire empty, full;
 
+    wire push = valid_in && ready_in;
+    wire pop  = valid_out && ready_out;
+
     VX_generic_queue #(
         .DATAW    (DATAW),
         .SIZE     (SIZE),
-        .BUFFERED (BUFFERED)
+        .BUFFERED (BUFFERED),
+        .FASTRAM  (FASTRAM)
     ) queue (
         .clk    (clk),
         .reset  (reset),
-        .push   (valid_in),
-        .pop    (ready_out),
+        .push   (push),
+        .pop    (pop),
         .data_in(data_in),
         .data_out(data_out),        
         .empty  (empty),