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/dffs.v

@@ -4,9 +4,11 @@ module dff ( input d, clk, output reg q );
 endmodule
 
 module dffe( input d, clk, en, output reg q );
+`ifndef NO_INIT
     initial begin
         q = 0;
     end
+`endif
 	  always @( posedge clk )
         if ( en )
               q <= d;