Add LED module and address decoding; disable LA

The Logic analyzer isn't that useful anyway since it does not track
rising and falling edges.

hw/efinix_fpga/addr_decode.sv

@@ -0,0 +1,12 @@
+module addr_decode
+(
+    input [15:0] i_addr,
+
+    output o_rom_cs,
+    output o_leds_cs
+);
+
+assign o_rom_cs = i_addr >= 16'hf000 && i_addr <= 16'hffff;
+assign o_leds_cs = i_addr == 16'hefff;
+
+endmodule