added attribute for maximum fanout for dp_rst

boards/uniboard2a/libraries/unb2a_board/src/vhdl/ctrl_unb2_board.vhd

@@ -306,6 +306,9 @@ ARCHITECTURE str OF ctrl_unb2_board IS
   attribute keep of led_toggle_red:   signal is true;
   attribute keep of led_toggle_green: signal is true;
 
+  attribute maxfan : integer;
+  attribute maxfan of dp_rst : signal is 1024;
+
 BEGIN
 
   ext_clk200 <= i_ext_clk200;