Add board-io, replace sevenseg in sw

hw/fpga/addr_decode.sv

@@ -5,7 +5,8 @@ module addr_decode(
     output logic rom_cs,
     output logic hex_cs,
     output logic uart_cs,
-    output logic irq_cs
+    output logic irq_cs,
+    output logic board_io_cs
 );
 
 assign rom_cs = addr >= 16'h8000;
@@ -13,6 +14,7 @@ assign ram_cs = addr < 16'h4000;
 assign sdram_cs = addr >= 16'h4000 && addr < 16'h7ff0;
 assign hex_cs = addr >= 16'h7ff0 && addr < 16'h7ff4;
 assign uart_cs = addr >= 16'h7ff4 && addr < 16'h7ff6;
+assign board_io_cs = addr == 16'h7ff6;
 assign irq_cs  = addr == 16'h7fff;
 
 endmodule