Allow initial blocks to be disabled during tests

Wrap initial blocks with a NO_INIT so that tests for archs without register initialization feature don't fail.

tests/arch/common/shifter.v

@@ -1,7 +1,13 @@
 module top(out, clk, in);
     output [7:0] out;
     input signed clk, in;
-    reg signed [7:0] out = 0;
+    reg signed [7:0] out;
+
+`ifndef NO_INIT
+    initial begin
+        out = 0;
+    end
+`endif
 
     always @(posedge clk)
 	begin