examples: ice_makefile_blinky: allow blinking with R, G or B easily

examples/ice_makefile_blinky/ice40.pcf

@@ -1,2 +1,4 @@
-set_io --warn-no-port led_green 39
-set_io --warn-no-port clk 35
+set_io -nowarn LED_G            39 # active-low
+set_io -nowarn LED_B            40 # active-low
+set_io -nowarn LED_R            41 # active-low
+set_io -nowarn CLK              35

examples/ice_makefile_blinky/top.sv

@@ -1,17 +1,21 @@
 
 module top (
-  input clk,
-  output led_green,
+  input CLK,
+  output LED_R,
+  output LED_G,
+  output LED_B,
 );
 
   localparam N = 22;
 
   reg [N:0] counter;
 
-  always @(posedge clk) begin
+  always @(posedge CLK) begin
     counter <= counter + 1;
   end
 
-  assign led_green = counter[N];
+  assign LED_R = 1'b1;
+  assign LED_G = counter[N];
+  assign LED_B = 1'b1;
 
 endmodule